The zoom thing works fine, just go to PC settings on the start button and then select System, top row left hand side, and the first page you see is for zoom. It works really well, it should default at 200% as a guess, it did for my Dell UP2715K 5K display. On a 3840px 4K panel that will give you the same "look" to the display as a 1920px FHD. If you are already at 200% display magnification and PS6 is still showing small UI components then make sure you have updated to the latest version, since PS6 has been around for a long time now, and if you are using an early version from disk it may not have the required support. If you have the latest update then unfortunately like my copy of LR4 it is not supported on UHD monitors and you will need to either upgrade to the CC package, or find a different program that does support UHD.
Alan