Firstly, when trying to log in, click here on ‘Forgotten your password?’.
On this pop up, add your username (this will usually be your email address) and click ‘Reset my password’ so that a code can be sent to you:
Enter the code you received via email, select a new password at least eight characters long (which must include at least one number, one special character, one uppercase, and one lower case character) and click ‘Change password’