You didn't mention what browser you are using, so I will just post the steps for two browsers where I know the exact procedure.
microsoft internet explorer:
1) Click the "tools" menu
2) Select "internet options"
3) Click the "content" tab
4) Click the "auto complete" button under the personal information heading
5) In the new dialog box, uncheck all the boxes under "use autocomplete for..."
6) Press the "clear forms" button
7) Press the "clear passwords" button
Mozilla Firebird:
1) Click the "tools" menu
2) Select "options"
3) Click "privacy"
4) Under the "saved form information" heading, uncheck "save information I enter in forms and in the search bar"
5) Under the "saved passwords" header, uncheck "remember passwords"
~psi42