Upgrading Nexus 5 from CyanogenMod 11 to 12.1
- On the phone, perform a Nandroid backup from ROM Manager
- Under Settings > Developer options, enable Android debugging
- Connect the phone via USB to your computer
- On your computer, run
adb pull /mnt/shell/emulated/clockworkmod/backup
- On the phone, turn off Android debugging
- Under settings > About Phone > CyanogenMod Updates, download the update and install it