The whole of Apple’s release notes for the update read as follows: “Fixes a bug that could impact Wi-Fi.” The update applies only to the iPad mini and iPhone 5.
To see the update, fast-acting iOS device owners initially at least needed to connect to iTunes. The built-in Software Update mechanism in the Settings app only coughed up a connection error. That issue has since been corrected; you can trigger the update by launching the Settings app, tapping on General, and then choosing Software Update.
Apple’s failure to provide more specifics on just what the Wi-Fi fix addresses means we can only guess at what issues the update really aims to correct. Some iOS 6 users have reported issues with cellular data getting used even when their iOS devices are connected to Wi-Fi networks. And on Monday, Apple released a trio of updates aimed at correcting Wi-Fi issues for newer Macs connecting to 5 GHz networks.
If you prefer not to update your device over the air, connect your iOS device to iTunes and follow the prompts.