Option 1: Lab 13 and you talk to the dude and say remove <skillname>
Option 2: Lab 13 and you say remove or forget and you lose ALL arch skills (not ideal since it will be a lot of exp

Option 3: You say remove or forget at the NPC that gave you the skill, he reminds you it will cost XXX exp, you then say confirm.
Option 4: Hand in the item for the quest again to remove the skill.
Option 5: A command players can use anytime /forgetskill NAME
I pref Option 3.