You can choose to leave a network you belong to anytime by going to Your Settings (by tapping or clicking on the gear icon from your profile) and selecting Account.
From here, if you choose to Leave this Network you will instantly leave the network and you'll stop receiving notifications. However, keep in mind that when you leave a network, your activity (such as any comments or posts that you added) will still be visible to other members.
If you want to permanently delete your account, just send us a note and we'll take care of it.
If you're logged in on the web, you can navigate to Your Settings > Account and use button at the bottom that says "Leave this Network."
How to leave a Group
If you only want to leave a Group that you belong to within the network, just navigate directly to the Group, open up the Group info tab and tap on the link that says "Leave this Group."