If you need to check the firmware version number of the Lumia 2520, you may do so by following these steps:
- Swipe in from the right to open the charms, and select Search. This should open the Search dialogue.
- Enter 'msinfo32', and tap the icon that looks like a monitor with the information icon.
- You should now be presented with the 'System information' application.
- The firmware of the Lumia 2520 can be found under the field 'BIOS Version/Date'.