Unhappy [Q] How to get rid of Lenovo P770 - Storage memory running out of space


I am new to custom ROMs installation. Can anybody help to eliminate storage space running out happening for internal storage.
Currently 2 GB allocated for internal memory but on same memory apps are installed and I am not able to move apps to USB storage.

Is there any way-out to merge internal storage and USB storage in to one single internal memory ?

Please help