It's a fairly simple thing to do. Remove the circlip from one side of the piston and using a drift that fits inside of the piston pin but not all the way through, push the pin out.
Back up the piston with your hand so that you don't put side pressure against the rod. Once the piston is off, the small end bearing will just slip out of the rod end.
When re-installing the wrist pin, be sure the pin fits correctly in the piston. The pin should slip into the piston with no resistance. You should be able to slip the pin in and out of the piston with your fingers. If the pin is too tight, hone the piston to a proper fit.
A tight wrist pin can cause your piston to seize.
Just my $ .02
