1) Buy the "seal removal tool" - it'll save the seal-lip around your wheels from screwdriver damage. get new bearing seals & grease.
2) jack up bike, secure it, remove a wheel.
3) remove bearing seal, remove bearings and spacers. WRITE DOWN OR PHOTOGRAPH where the spacers/bearings go from outside->in.
4) Clean the bearings in solvent - don't spin dry. Clean the races.
5) Get a big glob of axle grease (I use marine bearing grease) and put it in the palm of your "off hand" ( left if you're right handed )
6) grab the bearing, and dip it into the grease, kinda like of you were using a corn-chip to dig up some cheese dip. rotate the bearing, repeat until the grease is fully packed into the space between the inner/outer bearing shell.
7) Smear a little grease on the bearing races.
8) Reinstall the bearings/spacers in the proper sequence!
9) Use a big socket or a piece of PVC pipe as a drift, and TAP the seals into place. They should be about 1/16" below the edge of the bearing lip.
10) reinstall the wheels, making sure that you don't get grease on the brake rotors/pads.