If you're unsure what box model you have, go through the following steps:
Open the Main Menu
Select Settings*
From Information & Reset select Device Information
If you're not able to get into settings, you will be able to find the box model printed on the back or on a sticker on the bottom of the box.
*Depending on your box model, Settings will be on the last tab on the Main Menu or in a cog in the top right corner of the screen. You can get to the cog by pressing Up after opening the Main Menu. If you have the new Home Screen, you can access settings by pressing Up and then right after opening the home screen.