To add new "Payment Method" navigate from  Home>> Settings Tab>>Click on "Register Payment Methods">>Click "Add New" Button, as shown in the following screenshot below:

After you have clicked on the previous button it will display a blank fields both for "Payment Name", "Payment Display Name" fill in both of the fields and hit on the "Save" Button.

To be able to Edit a previous a Payment Method that has been created, simply double-click on the Payment Method that needs to be changed, after you have configured it do not forget to click on the 'Save' button.