Remove any items from under the sink
Place a bucket or towel under the drain
Locate the stopper linkage or lift rod under the sink
Disconnect the pivot rod or lift rod from the stopper assembly
Unscrew the retaining nut holding the stopper assembly in place
Pull the old stopper out from the drain opening
Clean the drain opening and remove any debris
Insert the new stopper into the drain opening
Reattach the retaining nut and tighten it securely
Reconnect the pivot rod or lift rod to the stopper assembly
Test the stopper by opening and closing it
Adjust the linkage if the stopper does not seal properly