You likely have purchased a retail demo unit with a special firmware. The hardware is (probably) identical to the regular tab 4, so you can just ODIN it back to the stock consumer firmware.
Instructions here, you need a PC and usb sync cable.
http://forum.xda-developers.com/tab-4/general/guide-how-to-restore-stock-firmware-t2979006
Download links for FW and drivers:
http://forum.xda-developers.com/tab-4/general/links-stock-galaxy-tab-4-firmware-t3013128