Dell U2913WM Monitor - Manual (Page 9)

Rotating Screen Content
Some Dell models provide Rotation features. On monitors with a Menu Rotation option under Other Settings in the OSD menu, changing the menu orientation will
automatically trigger a corresponding change in Windows screen orientation. On monitors with an Auto Rotate option under Other Settings in the OSD menu, enabling this
option will automatically trigger a corresponding change in Windows screen orientation when the physical orientation of the display is changed.