If you need to check the firmware version number of the Lumia 2520, you may do so by following these steps:

  1. Swipe in from the right to open the charms, and select Search. This should open the Search dialogue.
  2. Enter 'msinfo32', and tap the icon that looks like a monitor with the information icon.
  3. You should now be presented with the 'System information' application.
  4. The firmware of the Lumia 2520 can be found under the field 'BIOS Version/Date'.