Sorry for my ignorance but a picture is worth more than my description. My old plumbing has an 1.250" male stub out as you can see. I cannot tell if the nipple is threaded into the stub out....how would I change this to 1.5"?
As a plumber, the way to change to 1.5" tubular is:
open sheetrock
then see how much room there is
if enough room, couple to the existing 1.5" pipe
if not enough room, then Rambit out the stub and glue in a new stub