Turn off the water supply if needed
Place a bucket under the sink
Remove the P-trap
Loosen the drain tailpiece connection
Disconnect the sink stopper linkage if present
Unscrew the drain flange from above the sink
Remove the old drain assembly
Clean the sink drain opening
Apply plumber’s putty or sealant to the new drain flange
Insert the new drain body into the sink opening
Tighten the drain locknut from below
Reconnect the tailpiece
Reinstall the P-trap
Reconnect the stopper linkage if present
Tighten all slip nuts
Wipe away excess putty or sealant
Run water and check for leaks
Tighten connections if needed