How do you switch your account from one computer to another computer?
What do you mean by account?
You have to authorized the new computer and should deauthorize the old one.
iTunes Store: About authorization and deauthorization
iTunes: How to move your music to a new computer
Syncing to a "New" Computer or replacing a "crashed" Hard Drive: Apple Support Communities
iTunes Store: Associating a device or computer to your Apple ID
Retrieving data ...