Short Answer 
To adjust the brightness on your Apple TV, start by navigating to the Home screen and selecting the Settings app. Then, go to Display & Sounds, find the brightness slider under the Display section, and move it to the right to increase brightness before exiting the settings.
Step 1: Access the Home Screen
Start by using your Apple TV remote to navigate to the Home screen. You can do this easily by pressing the Home button on your remote. This will take you to the main menu where all your apps and settings are displayed.
Step 2: Navigate to Display & Sounds
Once you are on the Home screen, locate and select the Settings app. From there, look for the “Display & Sounds” option. Selecting this will open up settings related to video and audio output, allowing you to make changes to your display preferences.
Step 3: Adjust the Brightness
In the Display & Sounds menu, find the section labeled Display. Here, you will see a brightness slider. To increase the brightness of your Apple TV, simply move the slider to the right. Once finished, you can press the Menu button to exit the settings and enjoy your enhanced brightness.