I'm swapping out an old Peerless 2-handle shower/tub w/diverter tub spout for a Price Pfister 3-handle non-diverter tub spout. The problem I'm having is that I don't know how to get the old diverter tub spout "stub" off. The tub spout threaded off and the stub is too big to slid back through the tiled wall and I don't think it's threaded into the shower valve behind the wall. I've attached pictures of what I'm dealing with, any suggestions?
Thanks!

This larger brass piece in the posted phote slips over the copper stub-out. It may have small set screw on its side. Look closely if there is a small hole in the body of this brass sleeve.

Looking at the picture, it is pretty calcified. That's why it does not want to let go. Apply WD 40 and leave it over night. In the morning, take a large channel locks and try to twist it and pull on it. It will take some effort but eventually it will go. If it still does not go - take torch, heat up the 90 ell from behind and have somebody from tub side to pull on the copper nipple. You will have to then re-solder new piece of pipe on the same 90 ell to give you new spout outlet.

Thanks for the info Milo. There is no set screw on this "sleeve" and I even moved the o-ring hoping to find one under there (that's why the o-ring is out of the channel in the picture). I'll give the wd40 a shot and torch it out if that doesn't work.
Thanks again!