If your tenant's email changed, they will need to update their email from their Account Settings page. This will enable them to use their new email to log in and manage their payments. It will also automatically update their payment notification contact email.
If your previous tenant has moved out and you need to set up a new one, you can stop payments for your previous tenant and then click Invite a new tenant to change the primary tenant.
If you need to extend your current renter's payment term so they can continue to make rent payments, you can do so by selecting the Edit button next to your current payment period information. Then select the new payment end date from the drop-down menu. Alternatively, you can select No end date/Month-to-month if your lease is month to month.