Stuck at 3840x2160 resolution

[Danny001]

I have a dell up2414q connected to a MSI R9 270 via mini display port. I can't change the resolution of my desktop now. It's locked into 4k resolutions. It's the same when I play league of legends, stuck at 4k resolution with no other resolutions in the drop down menu.

How can I change my resolution?

 

[Outlander_04]

what happens when you connect another lower resolution monitor?