Updated to 7.0
Click on the Settings icon (the gear) located to the right of the search bar. This will take you here:
Within the horizontal navigation bar select Accounting. Then, select Payment Types. This will take you here:
Click the + Add button in the bottom right-hand corner.
Two boxes will appear. Click the box on the right to type in the description.
Click the box on the left to type in the name.
When done, click the Update button in the bottom right-hand corner to save changes.