There's nothing to convert. Both FP and EW applications produce HTML.
If you mean you want EW to convert Frontpage's non-compliant HTML to
standards-compliant HTML, that's where a little knowledge about HTML and
CSS comes in - EW won't totally do everything for you with the click of a
button, but one of its features is "Intellisense" which gives you pointers
and suggestions about the correct syntax (attributes and so on) for various
HTML tags and CSS commands.
Also, there are a few "housekeeping" commands that may go some way to
cleaning up the Frontpage extraneous code; in Code View, right click and
choose the "Optimise HTML" and/or "Reformat HTML" options from the menu.