I need to remove a hard wired smoke detector and want to know how to do it.

Most turn counterclockwise to remove. Very Likely.
Some have a lock. Not likely, If so, there is a slot on the side for removal, not likely. Then unplug detector, can remove 3 wire connector and cap wires or leave on, then cover.They make a round cover that is screwless. Clean look.
Smokes are required in each bed and outside of beds and on each lelel. I would not remove unless no longer a sleeping area(now an office?)

For safety, turn off breaker before working on smoke detector.

Chuck