Adjustable text sizes aren't new to iOS, but iOS 7 improves upon it with its new text size adjustment tool. In iOS 6, you could adjust the text in certain apps to appear much larger than the default. You can still do that in iOS 7, but you can also adjust it to be smaller, too, in any app that support iOS 7's Dynamic Type feature.
To change text sizes, make your way to the Settings app, tap General, then tap Text Size: You'll be presented with a slider that lets you adjust text size from tiny to quite large. Adjust the text to the size you want, then exit out of Settings. Any changes you make will take effect the next time you go to an app, so you don't need to manually close an app the reopen it for the change to occur.
If you would like to use text that's larger than the Text Size tool allows, you can do so through iOS 7's accessibility features. Open the Settings App, tap General, then tap Accessibility. Once there, look for Larger Type, and tap it. Enable the toggle next to Larger Dynamic Type, and you'll now be able to set even larger text sizes.
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