there are 2 different ways to delete an App:
1) t's easy to delete apps from the iPhone or iPad. Simply tap and hold on any icon for about 2 seconds - see them to start to wiggle and tap the X button in the left corner. that's it.
2) For devices running iOS 5 and later, there is also another way to do this is hidden in the Settings app, in the General tab, under: usage.
- you can manage the apps on your iOS device. Once there, you'll notice (after a certain delay if you have a lot of apps) that your on-board apps are listed in descending size order. That means: the apps that take up a lot of space will be listed first.
Tap on any app and you'll get even more info, including the version, the size of the app and the size of the Documents & Data. Just below that, you'll have a Delete App button in red. At the very bottom, you'll see how much space is available on the device itself.
Deleting apps that take up too much space is helpful when you're trying to install new apps, You may even notice apps that have a lot of storage attached to them that you weren't even aware of before like internet radio apps that sync songs to your device to play during the time you're not connected to the internet.
-- however, there are some core apps belonging to the iOS system and cannot be deleted like 'clock', 'calendar', 'contacts' etc.