When Re-Leased is synced with Xero, Contacts cannot be archived in Re-Leased. They can only be archived in Xero, and the synchronisation process will remove them from Re-Leased.
Archiving a Contact in Xero
Click on the Contacts menu and select the contact > select Archive.
The Contact will be Archived in Xero and only after the next sync of Contacts, will the the Contact be archived in Re-Leased.