How do I convert a propane furnace to electric?

There is NO conversion. You will have to buy a electric furnace to replace the propane gas furnace.

hvac1000 is correct. The only conversion is to yank out the furnace and replace it with an electric furnace and air handler. You'll probably have a large plenum void to fill.

Why are you looking to convert? And what are you utility costs and equipment costs that this makes financial sense?