To allow your church Treasurer to update billing information as well as print receipts for monthly charges they must first be added as a User or Admin to your contact list. Please note that giving your treasurer access to the billing information does not give them access to other owner privileges, such as removing contacts, curating content, changing the subscription and more.
Once registered, select "Organization Settings" after clicking "My Profile" in the top right corner.
From this page, you can search by name or email to locate your Treasurer, then click "Select" next to their name.
To remove them, simply click "Remove" listed next to their name.