This article speculates that you've already correctly installed ROMRaider onto your PC.

  1. Download and save your .xml to a KNOWN location on your PC.
  2. Open ROMRaider
  3. Navigate to the 'ECU Definitions' menu option 
  4. Select 'ECU Definitions Manager'
  5. Click the 'Add...' button
  6. Select the .xml you would like to load from your KNOWN download location
  7. Click 'Open'
  8. Click the 'Apply' button
  9. Click the 'Save' button

Lastly, attempt to open you ROM. While doing so, I generally check the 'Ignition Timing B' table to ensure that it appears to load correctly.