You have a rooted 4.4.2 (KitKat) Note 3.
Did you install a KitKat compatible recovery by flashing it with Odin (using a PC), as rooting it will not install one on it's own.
ROM manager is useful, but with a custom recovery installed (and you need it anyway, even with ROM manager) it is generally as easy turning the phone off completely. Rebooting into recovery mode by pressing and holding and in this order volume up, home and power. Press and hold them all until you get the splash screen and then instantly release them all. This will get you most of ROM managers features anyway, just not with a user friendly UI.
Recovery, depending on what type you have (stock is very limited) offers options to do a Nandroid backup (a "snap shot" of how your phone is at that point you can restore if things go wrong) and backing up your EFS folder, two things that are vital as flashing mods, kernels etc can mess things up. The "Nandroid" will get you working again and the EFS is needed (not a part of a "Nandroid") just the once only to restore your network/IMEI etc should you corrupt it.
I suggest reading up and understanding thoroughly what you want to do, remembering flashing a custom recovery will, without any doubt trip your Knox flag, and probably invalidate your warranty.
