Rules for abandoning/retraining class levels?

[SinsI]

To increase early game survivability, player that wants to play Wizard chose Barbarian as his first level, but his every level thereafter was a wizard.
After 7 levels of Wizard benefit from that early Barbarian level became insignificant, while the extra cost hurts more and more - that level of Barbarian kinda works like a Level Adjustment.
Now, there are rules for removing/reducing Level Adjustment - so are there any rules that would allow to either retrain that level, or even completely abandon it? Can you use, say, Negative Level to achieve that? Or maybe turn it into XP for crafting?

[Invader]

There's no mechanical trick or rule for retraining a class level. It's going to be up to your DM to just allow him to do it or not.

[Deophaun]

The PHB II (pg 197) has rules for Class Level Rebuilding. Basically, you can undertake a quest to reassign 1/5th of your character's level from one class to another. Instead of re-rolling hitpoints, you adjust HP up or down 1 HP per die difference per level.

[Invader]

The PHB II (pg 197) has rules for Class Level Rebuilding. Basically, you can undertake a quest to reassign 1/5th of your character's level from one class to another. Instead of re-rolling hitpoints, you adjust HP up or down 1 HP per die difference per level.

I stand corrected, I never realized you could do levels, I always just thought it was feats and certain abilities. http://blog.hughandcrye.com.s3.amazonaws.com/wp-content/uploads/2013/03/TheMoreYouKnowLogo.jpg