How to change apple ID on device

You should be able to log out of the currently logged in account by tapping on the id in Settings > Store (Settings > iTunes & App Stores on iOS 6), and you can then log in with a different account.

If you created a new account (as opposed to updating your existing account) then any content that you purchased/downloaded via the old account will remain tied to that old account, and only that old account will be able to re-download its purchases and download updates to its apps.

Using iTunes Match, automatic downloads, or re-downloading an account's past purchases could tie the iPad to the account for 90 days : http://support.apple.com/kb/HT4627