Default [q] lg p765 downgrade

my mobile having problem with ram
when i upgraded from ics to jb its showing ram 500mb used out 700mb
so i want to install JB offline which is 20v00a
when referred yo site guide for downgrading its not working
its showing some tool is having problem with windows like closing program???
and am havin 20v00_c version JB
Is downgrade require internet connection??