How would i add a gui that pops up on a players screen after i exit ROBLOX studio?

There are a few ways to do this. The most obvious would be to use the marketplace service, to get the ProductInfo on the place itself (in a loop), and compare the information to a variable set at the start of the server. I believe it is the updated or created value of the productinfo which you would need to check (although Roblox might have changed that recently).

Alternatively, you could just use what many others do, and create a "Version" thing in the game's title/description, and update it manually when you update the server. And use a server script to constantly compare it to the preset value at the start of the server.

local Desc = game:GetService("MarketplaceService"):GetProductInfo(--[[PLACE ID]]).Description
local Original = Desc:match("Version: (%d+.%d+)")

while wait(1) do
    local Desc = game:GetService("MarketplaceService"):GetProductInfo(--[[PLACE ID]]).Description
    local Current = Desc:match("Version: (%d+.%d+)")
    if (Current ~= Original) then
        --Server has been updated...
    end
end

--[[
And in the game's description, you would have to write:

Version: 0.1

]]