If the login credentials you enter using the webfire login url do not match what you have entered into the desktop app it will lock you out. If you change your password, or we do it for you, it does not automatically update in the desktop app, you need to do this manually. Submit a support ticket to have your account unlocked.
Once support has unlocked your account to login again right-click the " black folder" icon in the task tray (Windows only) and click "Account", then enter your new credentials there and click "Login".
If it is not in your task tray, the webfire desktop app icon (black folder) is in the Programs Menu -> Start Menu -> Programs -> WebFire -> WebFire User
Or, on Windows 8 or 10, just search in the start menu for "WebFire" and Webfire User will come up -- click that, and it will be in the task area.
If you are a Mac user you will be automatically prompted to enter your new credentials.