once all the frets are level and the tops are polished lightly you need to re-crown them. This basically means making to tops round again. You can use a tipple edge file that has been modified to NOT to cut on the corners for this or, if your awesome, you can use a actual fret crowning file like the one in this pic.

There are two different fret sizes cut into this concave file hence the little > symbol.

Its a good idea to resarpie all the frets so that you can see how much a flat surface you have remaining while doing this. You don't want that flat surface to completely go away you just want to make it pretty thin before you start polishing.