When using the graphics
Raspberry Pi Configuration tool, or when using
raspi-config from the command line, the only option for setting the resolution is:
Default-preferred monitor settings.
In my experience, when connecting to the Pi while headless using VNC all of the options become available.
If that doesn't work, you can try changing the
hdmi_mode= part in the
/boot/config.txt file. Do that according to this page.