Edit the config.txt file

The config.txt file is read by the Raspberry Pi on boot and contains your RPi specific configuration, like, the overscan settings, overclocking, default video mode etc…

It's located on the filesystem at /boot/config.txt

Connect with SSH
Remount partition on read-write with Command: mount -o remount, rw /boot
Use nano to edit the file located at /boot/config.txt: nano /boot/config.txt
Now close and save the file with CTRL+X and reboot your Raspberry Pi