Are you using the Dell Display Manager software? On my Dell UP2715K monitor it allows you to change the screen resolution, brightness, and also swap between various different colour profiles on the fly. I have it on and use it to switch between using the hardware AdobeRGB (99%) and sRGB (100%) profiles when changing between programs. I have AdobeRGB for all the Adobe programs, and then swap to sRGB when I change to a browser, since that is simpler with all the untagged images that are out there. Even if the browser is colour managed.
For some of the system programs though it will only allow you to run it's "Standard" profile, which seems to not be calibrated at all, and has a very noticeable tint compared to AdobeRGB/sRGB. Sometimes it takes a moment to swap for me, so if you have that it might be that it is hanging.