If you are logged out and need to reset your password, you can do that here: http://www.stockopedia.com/auth/forgot_password/
Alternatively, if you are logged in and want to change your password, you should click on the "Account Settings" tab of your Profile (this can be accessed by clicking from the "You" part of the main Header drop-down at the top of the page). That path will take you to the following password reset form (this is just a screenshot, though).
If a password reset doesn't work, you might not be activated. Check for an activation email from us when you registered and click the link. If all else fails, you can raise a support ticket via the Green Support Messenger asking for a password reset or manual activation. If possible, please specify your username so we can find you more easily.