Samsung Galaxy S III User Manual page 73

Update Your Phone's Software
Once you have backed up all your data, use the Update now option to update your phone's software.
1. From home, tap Apps
2. Tap Update Samsung Software.
 Your phone automatically downloads and installs any available updates. You may be
required to power your phone off and back on to complete the software upgrade.
– or –
Basic Operations
> Settings > More tab > System update.
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