i have the same phone zte , i took it to carrier what they did reset the phone to the original reset like when you got the phone deleted all the file you downloaded it works for a while then i started downloading stuff and that take a lot of memory . this message appear on your phone whenever you downloaded too many program .if you want to set your phone to manufacture reset safe your phone contacts and your video and pictures to your SD card .if you don't know how take it to your carrier he know how to do it for you . go to setting then look for reset to manufacturer, good louck