Upgrade iPad with iOS 5.1.1 to iOS 7
What ipad do you have?

I will explain the options you have:

1) does your ipad have a camera? If not you have the first iPad and the latest iOS version than is iOS 5.1.1

When your ipad has a camera, you have two options i believe:

1) go to settings > general > software update. The app will then show the latest iOs version available for your device. 

A download &amp; install button (not sure if it displays 'install' but i'm sure about 'download') will show up and you can tap that to upgrade your iOS versions.

2) connect your ipad with your charging cable (lightning or 30-pins) to your computer

Open itunes, or download it from apple.com, when your iPad is connected it will be opened in itunes.

Click the "search for updates" button and follow the on screen steps