You can prune a rose bush anytime of year.. Prune back to just above a five leaf set, OR a new nub on the cane. You should cut at an angle about 1/2 - 3/4" above the nub or leaves with the angle of the cut sloping away from the set or nub.
Treat with some good rose food/ systemic fungus and insect control, and about a 1/4 cup of Epsom salt.
Of course this only applies to "everblooming" roses, if you prune back a seasonal bloom bush you'll be pruning back your only batch of flowers. Personally I'd wait for the first bloom to pass, then prune it back to where you want.