Can landlord change the locks?

[Sandra N.]

An elderly lady I know filed an eviction concerning a commercial bldg. she owns. A barber shop to be specific. Landlord and tenant went to court. Got the judgment and tenant was ordered to vacate the premises last Thursday. The tenant is still there and the elderly lady's son wants her to change the locks and not file a Writ of Possession. The son thinks his mother has the right to retain everything in the barbershop since the tenant owes his mother over $6k in back rent. Is her son advising her to do something illegal even though the elderly lady got the judgment in eviction court? If she decides to change the locks, would she need to post a notice on the window? Just wondering.