Remove the outer wheel bearing, reinstall the retaining nut. Then grab the drum and yank it off. The seal and inner bearing will stay on the spindle.
Pack up your new bearing with grease. Pound out the outer race in the drum with a punch and hammer. Reinstall the new one with the same tools.
Then place the new bearing in the new outer race and use a hammer to install the new grease seal.

Lot's of times I can reuse the grease seal because I don't damage them yanking them out like I described.

Good luck, do it it's a easy job.