From the intro page, the user account details page can be accessed by clicking the Account button in the upper right corner. In other pages, the button is shown as a profile silhouette icon.
The Account Dashboard page shows the user's name, email and organization (optional). Buttons next to each provide the ability to change the username, email, or password. Currently, only a password change can be done only by the user. A username or email change takes a bit longer.
The Extensions button shows details and controls for use with the todoist extension (see this page for details).
The bottom buttons allow you to Exit the dashboard, or logout of your account.