From MEPIS Documentation Wiki
XRandr - The X Resize and Rotate extension
The xrandr command is run by clicking KMenu --> System --> More Applications, or from the command line (as user, not root):
-will list available display modes for your attached monitor/s for the current driver-hardware configuration you have.
To attempt to automatically configure all attached displays as one large desktop, type:
There are numerous possible configurations available using xrandr - including dual/multi screen, screen rotation, virtual screen - multi head etc.
It is possible to use XRandR to configure almost any display configuration desired and has a number of GUI front ends.