MLB.TV Help Center
How do I change the password associated with my MLB Account?
To access your MLB Account, click on the below image to launch the "Change Password" page. On this page, click on the arrow to bring up the password form.
In the window that opens up, enter your new password, in their requested boxes. Type your new password in both the "New" and "Re-type New" boxes to make sure that you have spelled each correctly and that the password boxes match. Your new password must be six to fifteen characters long, and contain only numbers and/or letters. Then click "Save."
You may also select "Forgot your password?" if you would prefer to have an email sent.
Once you have saved the new password, you can use it to log in to MLB.com.