The facility, on Lazy Hill Road, in Aldridge, will close its doors on September 17 at 5.30pm and reopen at 1pm on September 25.
The revamp will see changes made to the retail side, with an increased range of convenience goods.
Alternative post offices which people can use in the borough are Aldridge Post Office, in Northgate, and Walsall Wood Post Office, in High Street, Walsall Wood.
There will be new opening hours at Lazy Hill which are Monday to Friday from 9am to 5.30pm and Saturday from 9am to 12.30pm.
Scott Lacey, post office change manager, said: "We are making it easier for customers to get their cash, send and collect their mail and do their banking because we know how important these services are to local residents.
"We are confident that this new-look post office at the heart of the local community will meet customer needs.
"This modernisation is part of a major investment programme, the largest in the history of the Post Office and will secure services for the future."