If you have forgotten the password for your website, then this can be easily retrieved. Simply go to:
http://<website>/user/password
You can then reset your password by entering your username or e-mail address.
Only if you have forgotten your login AND changed your email address will you have a problem.
The emails sent to the user for password retrieval can be customised as part of the system configuration located at http://<website>/admin/settings/user
Exercise:

1. Logout
2. Enter the URL http://<website>/user/password
3. Enter your email address to retrieve your password
4. If possible, check your email account and follow the directions in the website email