I was firing my AR and the bottom blew out of the mag. Bullets, spring and follower went flying (downward).  I was able to remove the upper reveiver from the lower.  The bolt is stuck firmly in the upper.  I can see the star shape at the front of the bolt. I have been using wd40 to lubricate the bolt.  But nothing will free up the bolt.  Would someone tell me how to free up the bolt without doing damage.

thanks

Couple of questions.
Is it just the bolt, or carrier as well?
Is there a bullet still lodged in the barrel? Check by seeing if a wood dowel will go all the way to bolt face.
What type of ammo, and how many rounds fired before this happened?
What manufacture of upper?
From the sound of what you discribe, it could have been a overpressure in the chamber that caused this, and may require a AR specific gunsmith to fix and check for other damage.

I have a bushmaster rifle.  I fired about 30 rnds before this happened using reloaded ammo.  yes there is a spent shell in the chamber.  not sure what the charging handle is.

You should read technical note 49 at: http://www.armalite.com/.  

It could be the extractor is bent out preventing the bolt from disengaging the barrel extension.

Also take a look at "the dangers of cheap ammo" at: http://www.bushmaster.com/faqs/troubleshootingfaqs.asp#10