I might be wrong, but don't the buttons on the OSSC also help control some of the features?
I've always used a remote, but I think you should be able to use some basic functions?
Try playing around with the PCB Buttons -
OSSC Wiki - PCB Buttons - and see if that gets you where you need to be.
I really wish the BTN0 button was used to scroll through the menu and the BTN1 button was just an Enter button - odd decision there.
If you can get into the menu, I would recommend just going straight for the default settings with 480p Line2x - but also try enabling Upsample2x and scanlines (vertical or horizontal) to see if you like that look better.
As it is, the digitization of 480p content through the OSSC might already look better than normal, but...it's hard to say and depends on your TV.