This is a straightforward demo of how to disassemble, clean, grease, and re-assemble a skateboard bearing. Just in case you wanted to see it done. It's actually terribly easy if you've done it once.
Step 1: What you Need
Acetone or other solvent. (97% Isopropyl Alcohol is good too.)
A bowl or cup to put it in.
A small pin or straightened staple to remove the bearing shields.
Step 2: Pop the Seals
The seals can be popped out from the other side with a small pin or straightened-out staple. Stick your pin between the ball cage and the outside bearing race and press the seal out. Aim for the center of the seal, because it is made of metal and you won't puncture it.
If you've got metal shields, they're held in place by a circlip around the outside edge. Get your pin under one edge of the circlip and it'll come off easily. Then the metal shield just pops out. See this website for pictures of how to get the clips off.
Step 3: Soak and Clean
Alternately tap them on the bottom of the bowl and spin the bearings in your hand until they feel grit-free. Once you get a bearing cleaned, spin it dry and place it on a clean paper towel (balls down) to dry.
Repeat for the other 7 bearings.
While the bearings are finishing drying off, clean up the seals in the acetone. Be gentle -- you don't want to bend the inner metal ring.