I would not suggest externally cleaning your bearings and as paperclip32 mentioned removing your bearing cages is not advised.
Step 1: Removing Bearings
Once you have removed the wheels from the trucks the bearings should be removed by placing the wheel (with bearings inside) halfway on one of the trucks' axles' threading and pushing down on one side of the wheel.
Step 2: External Bearing Cleaning
Step 3: Final Bearing Cleaning
If you are using starter fluid like I am you should take your bearings outside and lay them on the ground and spray them down until they are clean and run like new again.
If you are using acetone, alcohol or a similar solvent you should place them in your bowl, or bottle, or whatever you use, and pour the solvent in and let them soak and shake them around.
If you are using a lubricant like Tri-Flow make sure you lay your bearings down on a paper towel and spray them down good so you can clean and lubricate them.
DO NOT USE WD-40! IT ATTRACTS DIRT WHICH CAN FREEZE OR JAM YOUR BEARINGS!