Updating OS on rooted SMP600

Hi, so I have a Samsung galaxy note 10.1 2014 edition and quite a while ago, I rooted it on Android 4.3, so it's stuck there. I'd like to upgrade to at least 4.4.2, but because I tripped the Knox trigger (I think?) I can't updates even with attempting an unroot. I've spent hours searching for a solution, but the best option I can find is the to find the OS I want and try flashing it? Is this correct and if so is there a free program I can use to do it? (Odin's on play store)
If someone could PM me links for relevant files, that would be very much appreciated.
Thank you!!