To change the password of cTrader account, go to “cTrader” and select “Sign in” and go to “Change Password” section.
By filing all the required section, you can update the password.
If you have lost the password, you need to check the email with login credentials in it or contact the broker.
In case of a Demo account, it could be expired after certain days and it maybe causing the error of login.
To open a new cTrader account, you may refer to the Comparison Table in the below page.