Advice about upgrading to iOS 7 from Apple:
Should I update?
Just because your device is compatible doesn't mean it should be upgraded right away. Once you update your device to iOS 7, there is no going back to iOS 6 or whichever earlier iOS you were running. (Yes, there are unofficial ways to downgrade, but these are not recommended for regular iPhone and iPad users.)
If you are not in a rush, wait a few weeks or months until Apple releases the first updated version of iOS 7. The early releases of the operation system can include bugs that should be addressed with subsequent iOS 7 updates. Let other eager people spend the next few weeks finding and reporting these issues so you don't have to deal with them.
Older devices can experience frustrating performance issues when upgraded to a new OS. The iOS 7 software was designed specifically for the hardware that's faster than your trusty old iPhone 4. If your device is anything older than the most recent generation, it might suddenly slow down, and battery life can suffer.
This should not be as much of a problem for newer devices, such as the iPhone 5, 4th generation iPad and iPad Mini, or the latest iPod Touch. If you are worried about performance issues, skip the update.
Updating immediately is recommended only for tech-savvy early adopters who are comfortable with the risks.