You can meditate to un-prepare a spell.
Prerequisite: Int 13
Benefit: You are capable of taking 15 minutes of meditation to “erase” a prepared spell. The spell slot the erased spell used to occupy is then open and can be filled with a new prepared spell. This feat is only useful to spellcasters who prepare their spells in advance.
Adventurer’s Handbook: Genius Guide Volume 1. Copyright 2010, Super Genius Games. Authors: Owen K.C. Stephens and Stan!