what if you add another variable to the mana, let's say manaRegen
you can make it boolean
so:
if mana < manamaximum, set manaRegen to true
if manaRegen is true, every 4 second add 1 mana (or maybe you want to use Wait, but I'm not really sure)
if mana >= manamaximum, set mana = manamaximum, and set manaRegen to false
I'm newbie so I don't really familiar with advance thingy, so I try to help with some basics...let me know if it works
cheers