Sign out of iTunes

To sign out of an iTunes account, open the Settings app from the iPad home page.

Scroll down and tap on the Store icon in the left-hand column.

Once you tap the Store tab, the current iTunes account will be displayed on the right-hand side as the Apple ID.

Tap on the Apple ID to bring up the options window.  Tap on Sign out.

Once you've signed out of the account, you won't be able to purchase any songs, apps or books until you've sign into another iTunes account.  Tap Sign In to add another iTunes account to the device.