Go on eBay and buy some heat shrink tubing that is large enough to cover the whole ESC because you need to remove it to see what is inside.
Take the heat shrink covering off. Determine which CPU type you have, generally Atmel or Silabs.
Google
rapid esc database
There are a lot of entries and links to pictures of the boards. Check pictures of all the likely (amps, CPU type, etc) candidates for one that matches.
When you test an ESC for the first time after flashing it use an automotive light bulb in series with your lipo. You should be able to run it at low power. If not you have possibly flashed the wrong firmware and powering it without the bulb will burn it out.