What do you 'purge iTunes enformation off cpu' ?
You can log out of an account on your computer's iTunes via the Store > Sign Out menu option. If you want to remove all of its downloads from your iTunes library then select them and press the delete button on your keyboard.
If you want to use the same email address on a new account then you will need to replace it on that account first (iTunes accounts can't be deleted, you can only stop using them) e.g. via the Store > View Account menu option on your computer's iTunes or via http://applied.apple.com