[HOWTO] Manually Update OTA 5.1.1 in a ROOTED LGLS996

I need to manually update my flex 2 from 5.0 to 5.1.1
trying to fix all lagging and overheating problems.
found a solution(sorry, can´t post links yet) but apparently only works in non rooted phones.
is there a way to do it in a rooted one?