In Internet Explorer 7: Click the 'Tools' menu. Select 'Internet Options' from the menu that appears. Click 'Delete...', beneath 'Browsing History' on the dialog box that appears. It will be in the center area of the 'General' tab. Click 'Delete cookies...' on the next dialog box that appears.
In Firefox: Click the 'Tools' menu. Select 'Options' from the menu that appears. From the dialog box, select 'Privacy' on the left. Find 'Cookies' on the main pane, and click the 'Clear' button adjacent to it.
In Safari: Go to Preferences, Security, then show Cookies and either select 'Remove all' or select individual cookies and then the 'Delete' button.
In Opera: Go to Tools, Preferences, Advanced, Cookies, Manage cookies then select the name of this site and click the 'Delete' button.
Your cookies should now be removed. You may want to restart the computer and revisit the forums to be sure