I've always puzzled over browsers of all types and why they don't allow us to manage login details and such. I assume it is a security issue to prevent access by unauthorised users from changing the details.
You could take the "Sledge Hammer" approach. Goto IE8 Tools > Internet Options, then the Advanced tab, and click the "Reset" button.
This resets IE8 to default, but that means you lose everything, all add-ons, all history, favorites, cookies, and login details. You can export Favorites before using it then importing the favorites back afterwards, but as far as I know, that is all you can do.
May be others here will have better news for you.
I want to clean up some wrong keystrokes in some of my stored passwords. I managed to delete all stored passwords, which is partially acceptable; I don't mind starting over. But all the user names are still in place, and I'd like to delete those and start over, too. How do I do this? And ideally I'd like the ability to edit stored user names and passwords one at a time. Is there any place in IE8 that allows me to do this? (I'm using Windows 8 on a Dell Inspiron desktop).