To remove silicone before it is cured you use a putty or other straight bladed knife to remove any of the uncured paste. Then wipe the area clean with isopropyl alcohol to remove any leftover residue.
After it is cured you should first you should remove as much of the silicone as you can with either a knife or a razor.
A solvent can them be used to remove any oily residue or any remaining silicone. It may be necessary to soak the silicone in a solvent overnight to break it down.
A list of solvents in the order of aggressiveness in attacking the silicone:
Paint thinner (mineral spirits)
When using solvents, as with any material, proper safety precautions should be observed. Material Safety Data sheets are available upon request from manufacturers. Similar information for solvents and other chemicals can be obtained from manufacturers.
There also are “Silicone Eaters” on the market now. The chemical composition is unknown, but are less messy and more expensive than some of the other solvents. Use according to instructions.