I found that the instructions found on LinkedIn via this Google search are all wrong, I’m assuming due to a site redesign since all of those questions were answer.

Try the following instead:

• Log in [of course]
• Click on Groups along the top row:

• Click the name of the group you want to leave.
• Click More… below the group title

• Click “My Settings” in the drop-down

• Click “Leave Group” at the bottom of the page