The 24" dell 4k resolution is quite high I think in the area of 185 DPI so the size of Photoshop UI will be quite a bit smaller on that display then you use to on your old 100DPI displays. Adobe added an experimental 2x UI preferences into Photoshop CC 2014. You may want to download and install a trial of CC 2014.... Old versions of Photoshop are not updated...
tq... guess I would do that.
I have found the way to get around this and the answer lies in the display adjustment for text and the icons... under the control panel.
This adjustment is global and encompass all software not only photoshop. Hence I hope Microsoft will look into this for 4K monitor users especially those with dual monitors with different K's eg: 4K and a 1920 panel.
Be careful in adjusting text size using Microsoft Text scaling. The fonts used in Windows desktop were designed for displays with a 96DPI resolution. You can scale up fonts using s couple of features Microsoft programed into windows. However if yuo increase the size of text too much in size text will not fit into areas allocated to hold the text.