To replace your old rusty drain cover. First, some masking tape over drain cover, to prevent screws from falling into drain. Sweep debris away, as so not to clog up the hole. Remove old shower drain cover to measure, take it to the store, to get the exact size. It's best to take along the screw too, just in case there isn't a screw thats of the same length. Chip away debris from old drain cover, as to make new drain cover fit in easily. If you follow this video, you'll able to replace your old shower drain cover with ease and properly.