Is it possibe to change a full wallet into a lite wallet?
yeah, delete all folder or rename it , the one contains all info and install new wallet "light" wallet this time.
It's not possible to change a full wallet into a light wallet (not in a straight forward way). Please don't delete anything unless you have a full backup (necessary to restore blackbytes) or the seed (enough to restore bytes).
What you can do is install a new light wallet elsewhere, then transfer your funds to it. Mind that by doing so, you'll have to link your new addresses.
Exactly what i said. if he rename it he can get access to it later. back up of whole wallet only possible with full wallet.
So one option is to install brand new wallet and move coins to there.