I'm assuming you mean it needs an ios upgrade. Connect it to a computer with itunes via your usb charger.
with itunes, click on your device when you see it come up. this should take you to your summary screen where you'll see a picture of your ipad and the serial number, you will also see an option for update.
If you mean you need iOS 6 - you cannot update the original iPad to iOS 6. If you want to update to iOS 5.1.1 then do this using iTunes on your computer.
Connect the iPad to the computer, launch iTunes. Select the iPad under the devices heading on the left, click on the Summary tab and then click on Check for Update.
You can read about it here.
If you have an iPad 1, the max iOS is 5.1.1. For newer iPads, the current iOS is 6.0.1. The Settings>General>Software Update only appears if you have iOS 5.0 or higher currently installed.
iOS 5: Updating your device to iOS 5 or Later
If you are currently running an iOS lower than 5.0, connect the iPad to the computer, open iTunes. Then select the iPad under the Devices heading on the left, click on the Summary tab and then click on Check for Update.
Tip - If connected to your computer, you may need to disable your firewall and anitvirus software temporarily. Then download and install the iOS update. Be sure and backup your iPad before the iOS update.