If you don’t want to perform an over the air update for iOS 5 Beta 5 then follow this simple guide on how to install it using iTunes. You can check the compatibility of iOS 5 Beta 5 from here.
Step 2: Plug in your device and run iTunes 10.5 Beta 5.
Step 3: Backup your device.
Step 4: Mac users should press alt and click restore while windows users will press shift and click restore in iTunes.
Step 5: Locate the ipsw file of your device and begin restore.
iTunes will take 10 minutes or so to install iOS 5 beta 5 on your iPhone, iPad or iPod Touch.
Note: If you are using a software unlocked or jailbroken device then stay away from the update. If you have a factory unlocked device then you may proceed without any worries.