You will be able to upgrade your Yakkyofy Free subscription by following these steps.
Please click on the icon at the upper right corner of the screen and select "Subscriptions":
You will see this page, on which you can select two billing intervals: Monthly (30 days) and Annually (365 days). The annual option will also allow you to save 25% of the subscription’s cost:
Then you should click on “Subscribe”:
On the following page you will be able to fill your credit card information and click on the highlighted button to pay the fee: