I hope TomMK doesn't mind me citing him here from another post:
TomMK schrieb:
-------------------------------------------------------
> You edit the first 3 lines of f1graphics.cfg as
> follows:
>
>
> 1 ; f1graphics.cfg controls all settings (default 0)
> 1920 ; Game 3D Horizontal Resolution
> 1080 ; Game 3D Vertical Resolution
>
>
> The GP4 menu will be at a very low resolution when
> you load the game, don't worry about this. The
> menu cannot scale to custom resolutions, but
> in-game it can.
This should solve your problem. Simply change the values to what you'd like to have the resolution.
GPGSL : Team Owner of 'Maverick Track Performance' (MTP)