Os 5.0.1

[ohsaa_referee]

How do I upgrade from 4.3.5 to 5.0.1?

 

[twerppoet]

Here is Apple Support page.

http://support.apple.com/kb/HT4972

I highly recommend you read this entire thread before beginning.

http://www.ipadforums.net/ipad-help/49411-ios-5-5-0-1-upgrade-troubleshooting.html

And in case it isn't mentioned, make copies of anything you consider important first. Email it to yourself if you don't have any other method.