Update

[eugenia]

There is software update available for my ipad, however on downloading, it does not update my OS.

 

[oberkc]

What is your current OS version? Are you attempting this update through iTunes?

 

[eugenia]

My current OS version is 4.2.1. Yes I am trying to download the software update for my iPad- via iTunes.

 

[oberkc]

I updated mine a few weeks ago, so my memory is quickly fading. I recall, in general, that it was pretty painless and intuitive.
Do you have the latest version of iTunes? I recall that this was necessary.
iPad is plugged in via USB?
I notice a procedure here:
[Moderator edit: Removed reference to external iPad-related site. Please, read the forum rules. Thanks.]
Hopefully, following this process solves your problems.

 

[twerppoet]

Try reading through this thread. Lot of explanations and troubleshooting tips.

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