Do I need a credit card to install free apps on my MacBook Pro?
Open iTunes.
From the Menu Bar, select Store > My account. You will be prompted for your Apple ID and Password. Enter it. 
Under “Payment Type” click the “Edit” link. 
Select “None” and then click “Done”


This will enable you to download free items without needing to provide any financial information. Obviously, if you want to purchase an app in the future, you’ll need to update your payment method.