If you want to leave a workspace, simply go to this workspace's settings page and scroll down the page.
N.B. You'll loose ANY membership on subjects from this workspace, even if you join the workspace again afterwards.Your tasks on this workspace will be deleted unless you give them to someone else before you leave, and you won't have access to anything from this workspace anymore.
What happens with the subjects I'm officer of when leaving a workspace?
Subjects you are the unique officer, will become "orphans" and any subject's member can become officer of these subjects.
Subjects with no members will be closed.