When you click on http://app.coursio.com/login to log in, make sure you enter your email address and new password manually in the login fields since your browser has a tendency to save old passwords automatically. If it still doesn't work, a tip is to clear your so-called cache memory. When you clear your cache memory, saved data that is otherwise filled in automatically disappears. If you use Google Chrome (which we recommend), this link goes through how to clear your cache memory step-by-step.
If you have saved login information that fills in automatically, you can click on "Use other login" which is under the login button.