The fields are stored in the registry here :

HKEY_CURRENT_USER\Software\Interwoven\WorkSite\8.0\iManExt\AutoCompleteEx

HKEY_CURRENT_USER\Software\Interwoven\WorkSite\8.0\iManExt\AutoComplete

You can delete these whole folders to wipe all the Autocomplete enteries

To modify individual items , you can go into each of the folders or use an f3 search to find enteries however the enteries need to be sequential so when you delete , readd the last item for that numbered entery , then delete the last item to stop duplication