Zte N9137 User Manual page 152

Problem: Cannot install applications.
Solution: Applications cannot be installed with only a
little free space on the phone or portable storage. To
check free space, see
Applications not supported by your phone cannot be
installed either.
Problem: Cannot unlock screen.
Solution: Power the phone on again. If you are unable
to turn the phone off, remove and replace the battery,
and then power the phone on again. Data that was
being edited is erased after the phone is powered on
again.
Settings – Device –
152
Storage.