Updated for 7.0
On the left-hand side of the screen in the navigation bar, select My Account. The page will look like this:
Select the Your Account tab.
In the horizontal navigation bar Click + Payment. You will find this here:
Once you have selected +Payment, you will be taken to a screen that looks like this:
If your billing address and card information are not already filled in, follow the prompts to add that information.
Click on each box and type in the respective information.
Type in the amount you are paying in the box next to the open invoice.
Click Submit Payment to finalize the payment.
These are samples.