If you have a coupon code for timeghost, you can redeem it in the Workspace/Subscription section of the Settings. If you scroll down to Management you can click the button Upgrade

After that you can choose between a monthly and a yearly subscription model. In the next step you can type in your code if you click on Apply coupon

In the next step you can Proceed To Checkout and then you have to type in you billing and payment details.