If it's some web site, you contact the host to reset it.
If it's some zip, word, PC password I've used www.lostpassword.com
Few years ago I made a page for our gamedev team called Seven Shapes Studios but we sort of had a three year hiatus and during that time the website we had (and to where the e-mail address was linked) closed. So now I don't have the password anywhere and the e-mail doesn't exist.
Is there any way to work around this?