HMD XR21 user guide

Tap Settings > System > System update > Check for update to check if updates are available.

When your phone notifies you that an update is available, just follow the instructions shown on the screen. If your phone is low on memory, you may need to move your photos and other things to the memory card.

Before starting the update, connect a charger or make sure that the device battery has enough power, then connect to Wi-Fi, as the update packages may use up a lot of mobile data.