Go to your group and to the left side column you will see a Tab: Quick Links: the 4th one down is Leave This Group click that.
at 9:44 PM on Jan. 10, 2010
Here's how to remove yourself from a group:
Mouseover the 'Groups' tab.
Click the 'My Groups' link on the left side of the page.
Go to the homepage of the group you want to leave.
Click the blue 'Group Settings/Leave Group' button.
Click on the blue button that says 'Leave Group'.