Why isn't the value getting doubled when I purchase the upgrade? [SOLVED]

There are a few things I noticed here that you could clean up. But first, I will address your doubling value problem. In your script, you never actually change the value of UpgradeValue. In order to change the value of a variable, you must first declare it then multiply itself by two.

UpgradeAmount = UpgradeAmount*2 --multiplies UpgradeAmount by 2

You should also move your variables declared on lines 2-6 into your function so that it doesn't cause too much lag, moving them into the function would cause your variables to change every time the function is called, not every 1/1000 of a second. Just make sure to declare them before you use them.

Another thing I noticed is that on line 9 you used Money.Value > Cost - 1. Which could translate to money is no less than the cost. For that we would use >= or greater than or equal to. Also, I recommend keeping your conditions in parentheses

if(Money.Value >= Cost)then

end

I also noticed how long your hierarchies got. You can use something similar to GCD (Greatest Common Divisor) to rule out things that they have in common, like how script.Parent.Parent and script.Parent are used so much. I assume that script.Parent.Parent is a part, and script.Parent is the upgrade, so we will define these two variables inside of your script

local upgrade = script.Parent
local part = upgrade.Parent

Now just replace your script.Parent.Parent and script.Parents with your upgrade and part variables. Other than that, you should be good to go.

P.S. I'm curious what SoundToggle is, could you please tell me?

Player = game.Players.LocalPlayer
    Button = script.Parent
    Cost = script.Parent.Price.Value
    Money = Player.leaderstats.Money
    UpgradeAmount = script.Parent.Parent.UpgradeIncome.UpgradeAmount


Button.MouseButton1Down:connect(function(purchase)
    if Money.Value > (Cost - 1) then
            Money.Value = Money.Value - Cost

            script.Parent.Parent.ClickForMoney.MoneyToGain.Value = script.Parent.Parent.ClickForMoney.MoneyToGain.Value * UpgradeAmount.Value

            local PurchaseCounter = game.Players:FindFirstChild(Player.Name):FindFirstChild("PurchaseCounterFor"..Player.Name)

            local TotalPurchases = script.Parent.Parent.Parent.TotalPurchases           

            print(

                "Cha-Ching! "..script.Parent.Name.." Was Bought By "..Player.Name.."! "

                ..script.Parent.Price.Value.."$ Has Been Charged From "..Player.Name..

                "'s In-Game Money! Enjoy Your "..script.Parent.Name..", "..Player.Name.."!"

                )

            PurchaseCounter.Value = PurchaseCounter.Value + 1

            TotalPurchases.Text = "Total Purchases: "..PurchaseCounter.Value

            local Sound = Instance.new("Sound")                 --The Cha-Ching Sound
            Sound.SoundId = "http://www.roblox.com/asset/?id=131886985"
            Sound.Parent = Player.PlayerGui.SoundFixGui

            local SoundToggle = game.Players:FindFirstChild(Player.Name):FindFirstChild("SoundOnOffFor"..Player.Name)           

            if SoundToggle.Value then
                Sound:Play()
                wait(1)
                Sound:Remove()
            else
                Sound:Stop()
                wait(1)
                Sound:Remove()
            end
            print("Money Increase Per Click Increased By *"..script.Parent.Parent.UpgradeIncome.UpgradeAmount.Value.." For: "..Player.Name)
    end
    wait(0.001)
        script.Parent:Destroy()
        print("UpgraderGui#1 Destroyed After Purchase By: "..Player.Name)
end)

Removed the repeat wait() and until

You can't do

if SoundToggle.Value then
                Sound:Play()
                wait(1)
                Sound:Remove()
            else
                Sound:Stop()
                wait(1)
                Sound:Remove()
            end

if the SoundToggle is IntValue

You don't have to do

game.Players:findFirstChild(Player.Name)

when you have the Player variable

There is no point of using

Button.MouseButton1Down:connect(function(purchase)

when you don't need the "purchase" variable MouseButton1Click would be better

I've checked it many times and it works for me.

Here is the whole script (Fixed)

Player = game.Players.LocalPlayer
Button = script.Parent
Cost = script.Parent.Price.Value

Button.MouseButton1Click:connect(function()
local UpgradeAmount = script.Parent.Parent.UpgradeIncome.UpgradeAmount
local ClickForMoney = script.Parent.Parent.ClickForMoney    
local Money = Player.leaderstats.Money  
 if Money.Value >= Cost then
   Money.Value = Money.Value - Cost

   ClickForMoney.MoneyToGain.Value = ClickForMoney.MoneyToGain.Value * UpgradeAmount.Value

   local PurchaseCounter = Player:FindFirstChild("PurchaseCounterFor"..Player.Name)

   local TotalPurchases = script.Parent.Parent.Parent.TotalPurchases           

            print(

                "Cha-Ching! "..script.Parent.Name.." Was Bought By "..Player.Name.."! "

                ..script.Parent.Price.Value.."$ Has Been Charged From "..Player.Name..

                "'s In-Game Money! Enjoy Your "..script.Parent.Name..", "..Player.Name.."!"

                )

            PurchaseCounter.Value = PurchaseCounter.Value + 1

            TotalPurchases.Text = "Total Purchases: "..PurchaseCounter.Value

            local Sound = Instance.new("Sound")                 --The Cha-Ching Sound
            Sound.SoundId = "http://www.roblox.com/asset/?id=131886985"
            Sound.Parent = Player.PlayerGui.SoundFixGui

            local SoundToggle = Player:FindFirstChild("SoundOnOffFor"..Player.Name)           

            if SoundToggle.Value == 1 then
                Sound:Play()
                wait(1)
                Sound:Remove()
            elseif SoundToggle.Value == 0 then
                Sound:Stop()
                wait(1)
                Sound:Remove()
            end
            print("Money Increase Per Click Increased By *"..script.Parent.Parent.UpgradeIncome.UpgradeAmount.Value.." For: "..Player.Name)
    end
    wait(0.001)
        script.Parent:Destroy()
        print("UpgraderGui#1 Destroyed After Purchase By: "..Player.Name)
end)

THIS IS THE SOLUTION

I do actually need all of the stuff you say I do not need, Vinteriss. Some of it is being used in other scripts as well.

I do indeed need the SoundToggle section. It's what makes it possible to toggle the purchase-sound.

It was kind of you to try to help me, Vinteriss, but before you answer of these scripting questions, I suggest you should check your facts, and how Lua works.

Oh, and I forgot to mention: I solved it on my own.

I had to make an individual IntValue for each player. Then when the player purchases the upgrade, it gets doubled.

Thank you to everyone who tried to help me.