Offline update for your iPad 2.
You must know which model of iPad 2 you have.
2.1 is WiFi only, 2.2 is GSM, 2.3 is CDMA.
Download the correct update (.ipsw) file from the following link:
Scroll down this page until you reach the section headed "iOS 5 direct download links".
You will get one of these files for each of the models.
These files are each over 700 Mbyte so be patient while downloading.
Remember where you save the .ipsw file.
Open iTunes and click on your device.
Hold the shift button down and click restore.
Select the update file and it will automatically update the software to your ipad.
If you do not know which model iPad you have, download all 3 .ipsw files.
iTunes will not update your iPad with the wrong file - it will tell you it is not compatible.
I hope this works for you.