How do I upgrade from 4.3.5 to 5.0.1?
This is a discussion on Os 5.0.1 within the iPad OS forums, part of the Apple iPad Discussions category; How do I upgrade from 4.3.5 to 5.0.1?...
Here is Apple Support page.
I highly recommend you read this entire thread before beginning.
iOS 5 and 5.0.1 Upgrade Troubleshooting
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.