How Do I Update a players leaderstats from a script?

Hello. Here I fixed your Script and I added Debounce.

local CoinWorth = 50
local WaitTime = 5
local Debounce = false

function onHit(hit)
	if hit.Parent:FindFirstChild("Humanoid") then
		local PlayerCharacter = game.Workspace[hit.Parent.Name]
		local Player = game.Players:GetPlayerFromCharacter(PlayerCharacter)
		if Player.Team.Name == "Red" and Player.leaderstats.Coins.Value >= CoinWorth and Debounce == false then
			Debounce = true
			Player.leaderstats.Coins.Value = Player.leaderstats.Coins.Value - CoinWorth
			wait(WaitTime)
			Debounce = false
		end
	end
end

script.Parent.Touched:Connect(onHit)

You tried to check player's team by player.Team == "Red". This is like you are trying to check a team name like this.

if game.Teams.Red == "Red"" then
	print("True")
end

Which is incorrect. You can do: if player.Team.Name == "Red" or if player.Team == game.Teams.Red.