Apple has released iOS 5 Beta 4 few mins ago and its now very easy to upgrade from iOS 5 Beta 3 to iOS 5 Beta 4. You dont have to download any packages as you do till previous beta upgrades. All you have to do is, visit Settings -> General -> Software Update to begin upgrading your iOS 5.
You may download the package iOS 5 Beta 4 if this is the first time you are going to try out iOS 5 Beta versions.
iOS 5 Over the Air Update
This simple feature reminds me the Android feature and still iOS 5 is trying to beat the comparison with Android features at the level best it can.