Q: How do I change my iPad from one apple ID to another already registered ID

Hi Mano11,

Welcome to the Support Communities!

The two articles below will explain all of your options:

Frequently asked questions about Apple ID

http://support.apple.com/kb/HT5622?viewlocale=en_US

An Apple ID is a user name you use for everything you do with Apple. Creating an account for an Apple service, such as the iTunes Store or the App Store, creates an Apple ID. Apple ID allows you to access other Apple services. You don't have to create a new account for each service—just use your Apple ID.

How do I change my Apple ID Name or personal information?

You can change your Apple ID Name at My Apple ID. Click on Manage your Apple ID and sign in with your Apple ID name and password. Click Edit and enter the new information, then click Save Changes. Changes take effect immediately. You can also use My Apple ID to change your personal information, such as your mailing address or email address. See Changing the name you use for your Apple ID if you'd like more information.

Using your Apple ID for Apple services

http://support.apple.com/kb/HT4895

Can I change the name of my Apple ID?
Yes. For example, if you get a new email address, you can change your Apple ID from your old address to your new address. For more information, follow the steps in this article.

Note: @mac.com and @me.com Apple IDs cannot be renamed.

I have purchased music, apps, or books with multiple Apple IDs. How can I get all of this content onto my iOS device?

First, you need to copy all of your purchased content so it is on the same Mac or PC with iTunes. This computer should be the one you sync your device with. For more information on how to move your content, see these articles:

• Mac:  iTunes for Mac: How to copy purchases between computers
• PC:  iTunes for Windows: How to copy purchases between computers

Next, authorize your computer to play content with each Apple ID in iTunes. Once your computer is authorized for all your content, it can be synced to your iPhone, iPad, or iPod touch.  

I hope this information helps ....

Have a great day!

- Judy