In iOS 7, you can change the size of text throughout your device. The only thing to keep in mind is that this only works on apps that are properly optimized for it. That means Apple’s first-party apps work, but anything else is up to the app’s developers.
Still, if you want smaller text (more words fit on the screen at once.), or larger text (for instance, if the current text is too small for you to comfortably read) you can go to Settings>Genera>Text Size.
There is a small block of sample text and a slider that enables you to change the text size.
This is for apps that support Dynamic Type. What’s cool is that you can leave this setting open and jump over to your Mail app real quick if you want to see what it looks like in an actual application.