1-Back up Your M7 Data First of all you need to
back up All your phone data 2-Enable usb-debugging
3-Download Rom Files
You can download Lollipop rom For
M7 form
HERE4-Copy Downloaded File to your sd card 5-Download Adb Drivers Here6-Connect your phone to computer or lap using USB Cable 7-Enter your phone into recover mode Use volume up then power button ( or use any App )
8-Choose Install zip file from sd card option And you done
XD