After skating for some time, dust and dirt gets into your bearings and clogs up. Sometimes water gets in and your bearings start to rust. You will find your skate's wheels not spinning smoothly. It's time to service those bearings.

Remove bearings from your wheels' hub using the tool provided by your skate manufacturer or similar tools.

Remove the C-clip that keeps the bearing shield in place. Use a safety pin (or a pen knife) to pry at the C-clip gap as shown in the illustration. Do the same for the other side.

Caution: Some C-clips can be quite tight and difficult to remove. Be very careful when handling the safety pin (or pen knife) and pry with care. Do not use excessive force as you might hurt your fingers.

Once you have successfully removed the C-clip, the bearing shield should come off easily. If your bearings are packed with grease, you might need some effort to remove the shield as the shield tend to stick due to the grease.

Once you have removed both the shields, soak the bearings for about 15 minutes in a cleaning solution such as Diesel or Sonic Citrus Cleaner. You might want to use a container with a lid so that you can shake it to effectively remove dirt and grease from your bearings.

Remove bearings from the cleaning solution and dry them with a cloth or paper napkins. Before you lubricate your bearings, you might want to condition them with anti-rust agent such as WD-40. Spray your bearings with anti-rust agent and let them soak for about a minute then dry with cloth or paper napkins.

Replace the bearing shield on one side of the bearings. Remember to secure shields with the C-clips.

Lubricate the open side of the bearings with your favorite lubricant. Just a drop or two will do. You may use any type of light lubricants such as grease, gel, or oil. My favorite is Slick-50, an engine treatment lubricant designed for automobiles. For best performance, you might want to use special lubricants designed for skate bearings, such as Sonic Super Oil/Gel, Blood Drops, etc.

When you have lubricated all your bearings, replace them back onto the wheels with the open side of the bearings facing inwards.

Put them skates on and enjoy the speed. :)