Games Screen Resolution Problem (RockNES Emulator)

When I change the resolution of the Emulator maximised the games resolution does not change with it/the game does not fit on the Emulators resolution. The game is stuck in the bottom right hand corner of the program. There is an option to change the games resolution too but that doesn't help, it just makes the games screen bigger but still in the corner. I've only tried Super Mario Bros. so maybe its only on that game but I don't think so.

Can anyone help?