You can change email address and password on your profile when you have logged on to your profile
https://candidate.webcruiter.com/en-gb
You find the options under the menu in the right top corner. You can't change to an email address that is already in use in Webcruiter. It has to be a unique email address and you need to click on the link in the email that you recieve in order to confirm the change.
Change password: you need to enter your existing password and then create a new one.