Kohler STERLING 402040 Homeowner's Manual page 5

Replace the Seal
Shut off the water supply to the toilet. Flush the toilet to relieve
water pressure in the flush valve.
Carefully remove the tank cover, and set it upside down on a
clean, soft surface.
Note the position of the colored buttons on the top of the flush
valve canister for reinstallation. Squeeze the tabs on both sides of
the canister, and pull the canister straight up and out of the flush
valve.
Remove and replace the seal on the bottom of the canister.
Reinstall the canister by pressing it into the flush valve so it snaps
into place.
Rotate the canister as needed so the colored buttons are in their
original positions.
Carefully reinstall the tank cover onto the tank.
Turn on the water supply to the toilet.
Flush the toilet several times using first one push button and then
the other to verify proper operation.
Check for leakage.
Sterling 5 1058763-5-A