My friend upgraded to a new phone, but it has less space than the old one
Mac or PC?

Because if you Sync'ed the phone with your computer it most likely copied the pictures to your My Pictures folder (PC) or into iPhoto (Mac). If you didn't sync the phone but just performed a backup then you will need one of the many utilities that let you browse/extract data from the backup.

I have not futzed with such a utility in many years I hear that iExplorer is a decent product. 

It should allow you to do just what you want on a Mac or a PC.