How do I root my Galaxy S5 SM-G900R7 version 4.4.2?

Re: Galaxy S5 SM-G900R7 version 4.4.2

That depends on the date of the kernel (Settings/General/About device/Kernel). If it's before June 3, 2014, use Towel Root. If not, wait for someone to come out with something that will work. (The exploit that Towel Root uses was patched on June 3, and I don't think anyone's written a later app that runs on the phone. iRoot needs a computer.)