To Sign Out from all Zoho Apps, click on the Profile link in the top right corner. You will see a drop down with an option to Sign out. Signing out will close all your other open Zoho applications in other tabs in the active browser.
Closing the account will close the Zoho account and terminate access to all the applications of Zoho. You will not have access to any Zoho applications. Only personal users will be able to close their accounts.
Only the admin can delete the the organization users accounts.
In case you have set up an organization account, and want to change your account to a personal account, or want to join another organizations account, you have to delete the current organization in which you have Super Admin role, before joining the other organization.