To stretch rock shoes that are just too tight, put them on and take a hot shower. Next, wear the shoes around the house until they feel like they have stretched. Stuff the shoes with newspaper to dry, and go climbing in them while they are still damp. Afterwards, re-stuff with paper.
You can stretch most shoes a full size using this method, although the amount of stretch depends in part on whether the upper is leather or synthetic and whether the shoe is lined. An unlined leather shoe will stretch more than a lined one, or a synthetic one.
Stretching shoes to this extreme can cause “rand bulge,” where your foot is so crammed in the shoe it presses against the rand, forcing it to bulge out and over the edge of the sole, compromising edging ability.
A better route is to get shoes that fit snug, but not overly so in the first place. Still, the warm-water stretch method does work well for softening a shoe’s hot spots, and speeding up a tight shoe’s initial break in period.