Apple has an age-based rating system to help parents identify and block inappropriate content. Most apps note the recommended age in their Rating section, along with descriptors that let you know what type of content you might find inside. To limit application access, go to Settings: General: Restrictions. In this screen, you can disable the ability to install apps and purchase in-app content. Select Apps to choose which app ratings A you'll allow.
As with desktop software, iPhone developers regularly upgrade their apps to add new features and fix problems. Your device detects updates for your installed programs; a red count badge on the App Store icon shows the number of updates available. Launch the App Store and tap the Updates section of the App Store window to choose whether to update one or all of your apps to the new versions. You can also update your apps from the Applications section in iTunes; the updates will transfer to your iPhone the next time you perform a sync.
To remove a third-party application, you can tap and hold its icon. The icons will begin to dance on the screen, and a black X badge will appear in their top-left corners. If you tap that X, you'll be asked if you want to delete the application. Because applications must store all their data in the app's package, deleting an application also deletes all its settings and stored information. If you delete an app that you wanted to keep, you can resync it from iTunes.
However, that app's data is gone for good. If you deleted it from iTunes as well, you can redownload it for free (unlike media) from the iTunes Store; you can load applications onto as many iPod touches and iPhones as you want, provided they're synced to your iTunes Library.