how do u replace a toilet u bend?

A difficult one to answer without seeing the job.
e-mail me with a rough sketch what the pan fitts into now
ie: a cast iron collar or a plastic collar with rubber vanes inside.
If the latter it could be a short /long spigot with a sealing collar with about 4 layers of rubber vanes. This is a commong repair fitting with the spigot size made so it's a neat fit into existing pipework. Most plumbing shops are very helpful if you explain the situation.
I assume the tiler had priced up for removal and refitting the toilet pan and cistern, in which case he/she is liable to re-seal the toilet pan as part of the work

e-mail me at robertwhiting76@hotmail.com
and I will send details of the fittings that you may need taken from the Osama waste and drain fitting booklet I have. In you sketch don't forget to show if the bend faces the wall (P Trap)
or faces the floor (S Trap). I check my e-mails daily and will allow until 24th March after I will not be checking daily as I would assume you've done the job.

20 toilets DIY'er retired.
March 2005