manually upgrade from 4.4.4 (.157) to 5.1.1 (.368) with flashtool without losing data

Hi, I'm currently in stock rooted .157 firmware with some mods installed (xposed)

i want to upgrade to .368 firmware without formating losing data on my phone and keep apps installed

maybe i'll need to re-root the phone and upgrade some modules to the lp version

any way to do this ? i really don't want to formate /data and reinstall all from the begining

any advice is welcomed :)

EDIT:

i want to upgrade with a stock rooted ftf file