Step 1: To replace your worn toilet tank flapper, begin by shutting off the water supply. Flush the toilet to empty the tank and carefully remove the tank lid. Set the lid somewhere safe. The lid is very fragile and nearly impossible to replace, so don't break it.
Step 2: Unhook the flapper chain from the end of the flush lever and remove the old flapper. Old flappers can be very gooey, so put on rubber gloves or grab a cloth before removing it.
Step 3: Take the old flapper with you when choosing an appropriate replacement. In today's market there are lots of options available, but basically if it looks the same, it's the right one. I recommend spending a little more and upgrading to a longer-lasting flapper. These are usually red or green and are guaranteed to last five or more years.
Step 4: If your old flapper attached to the overflow tube with side tabs, you may need to snip off the adapter ring between the tabs on your new flapper. Be sure to center the flapper over the drain hole to form a water-tight seal. Attach the chain to your flush lever and turn the water back on.
Step 5: Check for leaks around the flapper. Adjust the chain so the lever does not hit the tank lid when you flush, but the flapper stays up long enough for the toilet bowl to empty. This may take some time, but there is a happy medium.
Step 6: Finally, replace the tank lid, flush the stool once more for good measure, and pat yourself on the back for a job well done.