First step to add users is to make sure you have multi-user account enabled. If you don't, please contact us and we can make that change.
Once you have a Multi-User account setup, you have the ability to add licenses to your account to add users. To do this, simply click your email at the bottom of the left-hand navigation menu and select My Profile -> Licensing. Extra users are pro-rated based on term remaining.
After your purchase is successful, click here for instructions on how to set up the additional user in your account.