If you're on MF9 full rooted you can update your firmware/modem following Unknownforce's instructions.
HOWEVER PLEASE take heed about the MJA(MK2 too) Notes: ...
some people report better success with turning Auto Reboot and F. Reset Time unchecked. Do the same flash, but when you see PASS on Odin, unplug the phone and Hold the Power key for 10 seconds to reboot.
And read through the whole post not just the OP. Some people had to flash it a few times to get it to show up (in system info) properly - mainly because they didn't
follow directions precisely and skipped the note part on MJA/MK2.
Since you're now on MF9 fully rooted (stock) you can install yourself a custom recovery (Philz or TWRP - the latest Philz;philz_touch_6.08.9-jfltespr, seems to be the most reliable for now) and flash some ROMs. Virtually all of the 4.3/4.4 ROMs require the MK2 modem so know that too.
One thing I would highly recommend is to spend some time reading through the sections to get a clearer understanding of how this device behaves vs others (HTC, Moto etc.). Every device has it's peculiarities and caveats and not paying attention to them could ruin you day.