The best way to loosen and remove the seat post from your frame is to:
1) Remove the wheels, front fork, and handle bars from the frame (for convenience).
2) Turn the bike upside down and place the protruding part of the seat post in a bench mounted vice.
3) Turn the bike frame back and forth around the seat post. You should have the proper leverage with this technique to loosen the seat post.
You may be tempted to use a vice grips to grab onto the seat post and twist like hell. Let me save you the aggravation - forget the vice grip approach.