How to root / update the fake Lenovo P780W
Most Chinese fake phones can easily be rooted as they do not carry any bloatware, skins, extra bundles etc. These phones contain a near stock version of android and thus, don't cause any problems (usually) while rooting. You should be able to use cyanogenmod, it usually works very well on Chinese phones.

Best of luck.
Rahul.

PS: To be on the safe side, remember to take a backup.