Use FramaRoot - here http://www.framaroot.org/322-zte-v795/ is a complete tutorial and APK (or installer) download links. Download any one of those APK files listed there. Let us know should you still have issues. After root, you can then download Link2SD and move virtually all your downloaded apps from the phone storage to the External SD card storage. This will then resolve your 'Low disc space or insufficient memory" issue.