The easiest and best way to upgrade the iPad is to connect it to your iTunes and, after making a backup first (just in case), click on the Upgrade button. iTunes will do its "magic" and, after a few prompted inputs from you, you will end up with an iPad running the latest firmware.
Just be aware that the first generation iPad can only go up to iOS 5.1.1. The second, and subsequent, generation iPad will/can go to the most current iOS - iOS 6.1.3.
Hope that helps. Holler back if you need more assistance.
Marilyn
P.S. And where are my manners?! Welcome to the forum! It's good to "see" you and I hope you enjoy your visit(s).