Loosen and remove the pop-up ball rod nut. The rod and its attached nut, which protrudes from the sink drain pipe, is located below the sink to the rear of the sink drain pipe.
Pull out the pop-up ball rod from the rear of the drain pipe. This pop-up rod is what raises and lowers the sink stopper that is located inside of the drain pipe.
Remove the sink stopper from the top of the drain. This is done easily by hand.
Place the new sink stopper into the drain so that the loop at the bottom of the stopper aligns with the pop-up ball rod.
Insert the pop-up ball rod back into the hole located at the back of the sink drain. Make sure that the rod end slides through the end hole of the sink stopper.
Tighten the pop-up ball rod nut back into place over the pop-up ball rod. Apply plumbers tape on the thread of the drain pipe to prevent water leakage.