I don't have 'software update' listed under my general setting

The software update button weas only added in iOS 5.

This Article explains the steps you need to take.

iOS: How to update your iPhone, iPad, or iPod touch

http://support.apple.com/kb/HT4623

Scroll down to the section titled: Update your device using iTunes

If you can't see the left side panel, you can enable it by pressing control + S on windows, or option+command + S on a Mac.

Ignore the instructions for doing it from the device itself, scroll down, and follow the ones for doing it from iTunes on a computer.

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If you have an iPad 1, the max iOS is 5.1.1. For newer iPads, the current iOS is 6.0.1. For the iPad Mini the iOS is 6.0.2. 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

http://support.apple.com/kb/HT4972

How to install iOS 6

http://www.macworld.com/article/2010061/hands-on-with-ios-6-installation.html

iOS: How to update your iPhone, iPad, or iPod touch

http://support.apple.com/kb/HT4623

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 an iPad (except iPad 1) to iOS 6.x, the next update can be installed via wifi (i.e., not connected to your computer).

 Cheers, Tom 😉