With Linux, it is not as straightforward to understand where the settings are to adjust the screen size to match your HD/4K TV. Most of the time the firmware will detect the size and resolution of a TV but for those who want to manually adjust the size, here is how.
Step 1. At the bottom of the main screen, you will see the SETTINGS cog. Scroll down and select it.
Step 2. From this window choose VIDEO OUTPUT
Step 3. You can now adjust the Resolution, refesh rate and othe deisplay options
Step 4. Once chosen, the screen will go blank for a number of seconds. If the resolution is not compatible with your screen, it will revert back to the previous resolution.