Depends how you're replacing it, what you're replacing it with, and what tools you have or have access to.
The 'standard' way of replacing it would be to remove the TTB entirely, put each one in a press, press the old bushing out, and press the new one back in.
With hand tools, you can cut into the bushing with a saw, drill out the rubber part, burn the rubber out with a torch, then bang out the metal sleeve with a sledge hammer or try pushing it out with something like a ball joint press.
If you're replacing the entire bushing along with the metal sleeve that it's in, it'll be a heck of a job. There are polyurethane bushings that just press into the stock bushing sleeve though, so you just remove the stock rubber bushing and the small metal insert, which makes it a lot easier for DIY work.
http://www.explorerforum.com/forums/showthread.php?t=208039