Uninstalling NAV without password

I have an Nt workstation and it has a Norton Anti Virus (NAV). I want to uninstall and reinstall McAfee but when I tried, it is asking for the password to uninstall. I forgot the password. Please help on how to uninstall it? I tried deleting the NAVdirectory but it always says it is shared. What service should I disable to delete the directory and after deleting it, what other things I need to do in the registry to avoid pop-up errors?