I wish we could organize our spell book. As we progress, there"s little need for the early level spells that take up slots and do very little, if anz damage, or effect on an encounter.
So far, I have not seen a way to organize spells, but if you left click on a spell, you'll discard it much like in Wizard101. However, you'll have to wait another turn first before your spell hot bar 'refreshes' and 'shuffles' your other unused spells back into your selection.