Help LG G3 , Stuck on android 4.4.2, No updates

Hi I bought a refurbished LG G3 F400K (32GB) and it's an unlocked phone. But it was under a carrier called olleh. Still there are even some olleh software which i can't remove from the phone. But my phone works with local networks without any issues. But i can't even update it to android 5.0 ! Says my phone is already up to date !! I found a way to install android 6 using LGUP. Will my phone break if i update it that way? Please help me

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