Even with the correct , errors happen.
For devices running older versions (4.4 KitKat or 5.0), jumping to 5.1.1 feels like getting a new phone.
If your device is stuck on an older version and the "Check for Updates" button does nothing, you may need to manually "flash" the firmware. This is common for older Samsung, Nexus, or Motorola devices. Nexus/Pixel Devices: You can find historical "Factory Images" on the Google Play Services developer site Samsung Devices: Many users use third-party databases like to find specific PDA/CSC codes for Lollipop firmware.