How do you multiply a value from an int external value?

I have been able to retrieve the value but I cannot seem to modify it (multiply to be specific)

Hmm, since you provided no code, it'll be hard to answer this. Say if you had a leaderstat value named "Coins", and you wanted to double the value of it for a specific player, it'd go as so:

game.Players.Shawnyg.leaderstats.Coins.Value = game.Players.Shawnyg.leaderstats.Coins.Value * 2

This is the best I can give you, since you weren't specific.