If you have the instruction/owners manual to assemble it then just un-assemble it in reverse. If you don't have the manual you can buy one for $9.95 on this site:
http://www.online-owners-manual.com/ggtl817040.html
My husband & I had to do this with a big gym system we were given. We used it for awhile, but decided it was way to big for us. We took it apart enough to get it out the door.