Spell Leveling

I've run into a problem with my spell system. A hero gets to pick what spells he wants from groups. So for slot one he can pick from Holy Bolt, Storm Bolt, Shockwave, and Chain Lightning. These are all 3 level hero spells but my problem is that I want the hero to be able to upgrade them through a Dialog. What I mean by this is the hero uses an item and a Dialog pops up thats says "Spell Slot 1" "Spell Slot 2" "Spell Slot 3". I cant seem to find out a way that no matter what spell he has in slot 1, when he clicks the Dialog button "Spell Slot 1" it sets the spell in slot 1 (x=0,y=2) to Level 2. Is there a custom script or anything that could make this easy?