You don't download iTunes onto the iPad - iTunes, along with the rest of the iPad's built-in apps, can only be updated via updates to iOS itself (the iPad's operating system), they can't be updated stand-alone. Have you downloaded and installed iTunes on your computer ? If you have then you can check for iOS updates for the iPad by connecting it to it, selecting it on the left-hand side of iTunes and then clicking the Check For Updates button on the summary tab on the right-hand side.
There is more info on updating your iPad under the Updating Your iPhone, iPad, Or iPod Touch section on this pge http://support.apple.com/kb/HT1414
The iPad manual can be downloaded from here : http://support.apple.com/manuals/ipad