As others have said, they're usually disposable. If not, or if you want to try cleaning them anyway, try putting them into a mesh bag or something similar, then put them in the washing machine on a gentle wash cycle and let them dry naturally.

Obviously, try this with a small amount first, so that if they don't survive the process it's not the end of the world. If you don't have a mesh bag, a clean sock should be ok, just tie the end closed.

You can wash them in the sink with warm water and a little bit of soap too, but it's more work. Just remember to rinse them thoroughly before they go back in your ears :)