Connect to iTunes on the computer you usually Sync with and “ Check for Updates “...
See the Using iTunes Section Here...
If it is an iPad 1 it will update to iOS 5... if an iPad 2 or later it will Update to the Latest Version which is currently iOS 6.x
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