I changed the siderails on my TSPP to the ones with the flipper button guards before I sold it.

Yes, remove the lockdown bar and playfield glass, undo the nuts on both sides of the cabinet near where the lockdown bar fits and remove the bolts through the siderails. The bolts can be quite tight in the cabinet. Try replacing the nut back onto the bolt a few threads and gently tapping it to free it off.

As has been said, you need to do the same at the other end of the siderails. You'll need to unlock the backbox and tilt it forward enough to remove the bolts past the backbox brackets. There are also two screws along the length of the siderails that need to be removed. The siderails should then come off fairly easily. Don't forget they have been in place since the machine was built, up to nine years ago.

I really need to do this on my LOTR, as the cabinet is just starting to wear around the flipper buttons.