First off, I would ensure that you are running the very latest version of iTunes on your computer then just do a sync with the computer (transferring purchases if it asks) to get everything in order. Now, in the middle of the main iTunes window on your computer, when your iPad is connected it should say something to the effect of "there is new software available for your device" all you need to do now is click to download and install and follow any on screen prompts.
Let us know if you run into any problems.
The Archangel