I have an iPad with version 4.2.. Bt I want 2 change it to version 5.11. How??? I dnt have "software update" in my settings. Help please.

The Settings > General > Software Update option only appears when you have iOS 5+ installed, if you have iOS 4 then you will need to do the update via your computer's iTunes.

Connect the iPad to your computer's iTunes and copy any purchases off the iPad to your computer via File > Transfer Purchases. You may also want to copy photosand any important documents off the iPad as well e.g. via the file sharingsection at the bottom of the device's apps tab when connected to iTunes, via wifi, email, dropbox etc - they should be included in the backup, but it's best to havea copy of them outside of the backup just in case. You can then force a backup of the iPad by right-clicking the iPad 'Device' on the left-hand side of iTunes and selecting 'Backup'.

Then start the update by selecting the iPad on the left-hand side of iTunes, and on the Summary tab on the right-hand side clicking the Check For Updates button

Updating to iOS 5+ : http://support.apple.com/kb/HT4972

A first gen iPad will update to iOS 5.1.1 (it doesn't support iOS 6), and an iPad 2 and 3 to iOS 6.0.1 (they are the only versions that are 'signed' by Apple for them).

You will need a recent version of iTunes on your computer, yes.

You need iTunes on your computer as stated in the Apple article linked by King Penguin.

Follow the instructions in the link posted above. For your convenience, I have re-posted the link.

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