Changing an int value in Replicated Storage not working (?)

First you have to be sure you make it a serverscript

But the actual problem is the game.ReplicatedStorage.Wave.Value will result in something like this for the script

local wave = game.ReplicatedStorage.Wave.Value
-- For the server: local wave = 0
wave = wave + 1
-- For the server: local wave = wave + 1 --> 1

But it won't change the value, to do this you have to have the variable as an object and change the objects value like this

local wave = game.ReplicatedStorage.Wave
wave.Value = wave.Value + 1

Hope this helped, if you have any more questions, just ask :)