Software updates from Nokia are safe to install, and your settings, apps, photos, and text messages remain safe and sound. However, it is also recommended that you create a backup before doing a software update. Depending on your model you can do that from Settings > Backup > Create backup or from Settings > sync & backup > create backup. This will create a backup of the phone settings and personal content to the memory card.
The size of an update package can be several megabytes, so to keep the data costs down we recommend that if your phone supports it you use a Wi-Fi connection to download the update. Nokia software updates are free of charge but if mobile data is used to download the update, data transmission costs may apply. For more info on the possible costs, contact your network service provider.
Before starting the update, make sure your phone has enough battery power. If the phone battery level is too low, your phone will prompt you to charge the battery before starting the update.
Check that your phone is set to the correct date and time. With a wrong date or time, your phone might not be able to access the updates.
In case there is not enough free space on the phone memory to start the update, you will be prompted to free up space. That can be done by removing some apps or other large items, or moving them to the memory card.