PetrusOctavianus: Get an old CRT monitor and you will avoid those offensive black bars while at the same time prevent stretching of the image.
Or use a HD mod.
jarl_648: \
i got this HD mod but i dont know what resolution i should put. i got 1920x1080 on system, but when i write this resolution in HD mod its even worse-everything is really small and cant see hero...
That's because the 800x600 was stretched to fit the screen and so appeared bigger, while 1920x1080 images will be true pixel-to-pixel size.
If you really want the black bars to disappear
and keep the image non-stretched
and make it "bigger", then choose a resolution that is smaller but of the same 16:9 ratio, like 1280x720 or 1600x900 (and make sure your monitor/GPU scales it instead of centering it, which should already be the case, judging by the way you see 800x600).