The arcanist can prepare a spell in place of an existing spell by expending 1 point from her arcane reservoir. Using this ability is a full-round action that provokes an attack of opportunity. The arcanist must be able to reference her spellbook when using this ability. The spell prepared must be of the same level as the spell being replaced.
Pathfinder Roleplaying Game: Advanced Class Guide © 2014, Paizo Inc.; Authors: Dennis Baker, Ross Byers, Jesse Benner, Savannah Broadway, Jason Bulmahn, Jim Groves, Tim Hitchcock, Tracy Hurley, Jonathan H. Keith, Will McCardell, Dale C. McCoy, Jr., Tom Phillips, Stephen Radney-MacFarland, Thomas M. Reid, Sean K Reynolds, Tork Shaw, Owen K.C. Stephens, and Russ Taylor.