I can't find "software update" option on my iPad to update iOS

You need to use iTunes.

See the chart below to determine whether you can upgrade your device and what you can upgrade to.

IPhone, iPod Touch, and iPad iOS Compatibility Chart

Device iOS Verson

iPhone 1 iOS 3.1.3

iPhone 3G iOS 4.2.1

iPhone 3GS iOS 6.1

iPhone 4 iOS 6.1

iPhone 4S iOS 6.1

iPhone 5 iOS 6.1

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iPod Touch 1 iOS 3.1.3

iPod Touch 2 iOS 4.2.1

iPod Touch 3 iOS 5.1.1

iPod Touch 4 iOS 6.1

iPod Touch 5 iOS 6.1

-------------------------------------------------------

iPad 1 iOS 5.1.1

iPad 2 iOS 6.1

iPad 3 iOS 6.1

iPad 4 iOS 6.1

iPad Mini iOS 6.1

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Select the method most appropriate for your situation.

Upgrading iOS

1. How to update your iPhone, iPad, or iPod Touch

2. iPhone Support

3. iPod Touch Support

4. iPad Support

a. Updating Your iOS to Version 6.0.x from iOS 5

Tap Settings > General > Software Update

If an update is available there will be an active Update button. If you are current,

then you will see a gray screen with a message saying your are up to date.

b. If you are still using iOS 4 — Updating your device to iOS 5 or later.

c. Resolving update problems

1. iOS - Unable to update or restore

2. iOS- Resolving update and restore alert messages

If you have an iPad 1, the max iOS is 5.1.1. For newer iPads, the current iOS is 6.1.3. 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).

Tip 2 - If you're updating via wifi, place your iPad close to your router to preclude getting a corrupted download.

 Cheers, Tom 😉