can i upgrade ipad version 4.2.1 to IOS5?

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 yours is an iPad 1 then yes...

If a later model iPad then not any more...

iOS 4... See Here...

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

OR...

Connect to iTunes on the computer you usually Sync with and “ Check for Updates “...

See the Using iTunes Section Here...

How to update your iPhone, iPad, or iPod touch

If it's an iPad 1 (which if you are on iOS 4.2 then I assume that it is) then you should be able to update to iOS 5.1.1 (iPad 1 doesn't support iOS 6) - an iPad 2 can only be updated to iOS 6.0.1

To update, connect the iPad to your computer's iTunes and copy any purchases off the iPad to your computer via File > Transfer Purchases (File > Devices > Transfer Purchases if you are on iTunes 11). You may also want to copy photos and any important documents off the iPad as well e.g. via the file sharing section 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 have a 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

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

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

 Cheers, Tom 😉