If you do not remember your username, you can log in to your account by entering your email address in the "Username or Email" field. If you have forgotten your password, you can press "I forgot my password!" in the entry field of your account and then follow the instructions.
Once you complete these two steps, a message will be sent to your email with which you will be able to change your password. Please also check your spam folder, as it may be archived there.