Office 365 - Convert Mailbox to Shared Mailbox
1. Log into Office 365 portal (portal.office365.com)
2. Go to the Exchange Admin Centre
3. Go to Recipients > Mailboxes
4. Find the mailbox you would like to convert and select it
6. Wait while it converts to a Shared Mailbox
7. Go to the 'Shared' Tab and ensure you can now see the shared mailbox.
Optional: 8. You can now remove the license from the users account if not needed.
As you have to keep the user account please insure in the display name you add (Shared Mailbox) to the end so it is clear to see why that user account is still in office 365