If you are just a member, you can go leave on your own. Go to your coven's page and click on membership. You will recieve 2 options, leave your coven and go back. Select leave coven and you are done. If however you are a priest or priestess it is a bit more compilcated. You have only 2 ways to remove yourself from the coven. The first way is to step down and find an appropriate replacement for yourself. Promote them to council, then promote them as priest or priestess. However it is much easier to send a message to Pet and ask him to remove you, those are the only ways that you can remove yourself from a priest/priestess position.