To leave a site in Cloud that you are not the owner of, click the
Change site menu in the upper left corner of the interface. From here, you can hover over the site you want to leave and hit the
Leave site button. In the resulting popup, you will be asked to type a message to confirm the operation.
Once you've completed this operation, you've left the site and no longer have access to it. Other accounts within the site maintain the permissions they already had, including to content you may have created within the site. If you at one point want to rejoin the site, you will need to contact a site admin and request that they provide access.