I have searched for this question but I dont find any answer.
Why am i unable to change the fullscreen resolution when the option is there?
Have you clicked the Graphics button in Dolphin? Fullscreen resolution options should be under the General tab in the Display section.
Yes. I am pretty much able to change everything, except "backend", "render to main window" and "fullscreen resolution", which have no effect when I click on them. The current fullscreen resolution is 640x480, which would explain why the fullscreen image quality is miserable. The windowed image quality is good, though.
Make sure you're not playing the game while you try to change these options. They're blanked out when a game is loaded, even if you pause it.