Please follow the instructions in the following image:
Once you click on Upgrade Account you will be presented with the following choices:
Use the drop down to select one of the tiers we provide, select a subscription duration and click on the PayPal button to proceed with the payment. You will then be asked to login with your PayPal account or use your credit card (a PayPal account is still necessary however).
We also support payment via wire transfer - please email us at firstname.lastname@example.org and we'll provide the relevant details.