At the top, where it usually says "Join this Group," there will be a button in its place that says "Leave this Group." Click on it and then click OK when the next bubble pops up. That will make you no longer a member. In order to stop watching that group (have their art stop showing up in your inbox), go up to the very top right corner of your page - there's a button that says "friends." Click on it. It will turn into a pull-down menu. At the bottom, it will say "Manage Friends." Click on that, then scroll down to the name of the group that you want to get rid of. Next to it there will be a button that says "Remove." Click on that, then when the next box pops up click "OK."

Hope I was able to help (:

Of course