Can you change resolution, there is no option in game menus and didn't see this option In the config file either, I play in full screen ( have to everything is just too small otherwise ) my monitors native resolution is 1920x1080 and the game will play in lower resolution than that in fullscreen.

The creator made a change regarding resolution but I'm not sure if it's in the GOG version. It's in the latest version available on his site though.

And no, I don't think you can change it unless you change your desktop resolution. I play at 1920x1080 and it scales accordingly, it used to play at 1024x768 I think but not anymore.

This is a screenshot taken with the latest version at 1980x1080:
Unepic 1920x1080

I keep fullscreen and keep aspect ratio checked.