You could try pressing CTRL +
or CTRL -
and see if it changes resolutions for you. I'm not sure where the resolutions are defined, but I suspect X is selecting available modes from xorg.conf. On the other hand, it might just be a KDE illusion
but I do recall my monitor actually changing video-modes when using those key combinations.
Keep in mind, you will only be able to use resolutions which your laptop's screen actually support.