Currently Being ModeratedDec 9, 2012 7:11 AM (in response to Pawaranchn)
The original iPad will update to iOS 5.1.1. All other ipads will update to iOS 6.0.1.
If the version of iOS on your iPad is less than 5.0 there will be no update tab in Settings. To update these earlier versions of the iOS you need to connect your iPad to a computer and update through iTunes.
iTunes 10.7 or 11 is required to sync with your computer when your iPad is running iOS 6.0.1.
Currently Being ModeratedDec 9, 2012 7:25 AM (in response to Pawaranchn)
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
How to install iOS 6
iOS: How to update your iPhone, iPad, or iPod touch
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. After you update to iOS 6.x, the next update can be installed via wifi (i.e., not connected to your computer).