Goto recovery.
Take backup on external sd card
reboot
install
thisapk
Start the application and select the amount (I choose 2.5gb)
reboot into recovery mode
wipe data/factory reset
restore ur backup
reboot
connect ur phone to windows pc as USB storage
format the internal partition (be careful dont format sd card)
Now I have 2.5 gb internal, 300mb phone storage.
AND SUCCESSFULLY RESTORED MY OLD BACKUP.