Press it when you are in battle...(in other words when you are hitting people, not in pause)
Numpad 7: Add XP - each press adds more. This works when you are
actually in the battle portion of the game. Due to the way
the game works, it's best to only add 1000 XP at a time
which is the default amount. This basically allows you to
level up with the next kill.
You legend. I never knew I could click on it and change the value. Thankyou so much!.