I've done this on a not so precious frame, but if you value your bike,
take it to a shop with a proper press to avoid damage.
Pretty simple, but not for the faint of heart--mine required major
muscle to get in and out--but of course I did it via redneck
engineering: big ass screwdriver, mallet, block of wood.
Remove cranks, then remove circlips, then whack out crank spindle with
a mallet. Punch out bearings with a long screwdriver inserted in the
opposite crank spindle hole, assembly is the opposite of disassembly.
If I had to do it again, I'd have pressed the suckers in with a
vise/wood sandwich.
I used generic bearings from my local supply house, but Phil's are a
bit nicer. Mine were $5 per side, and I don't think the Phil's run more
than a tenner each. If your spindle is old or has a lot of miles, might
think about replacing it as well, as they like to crack around the
circlip groove.
Again, have your shop do this if you want to avoid dinging your frame
or breaking your seat tube cluster with that spare anvil in the garage.
