How to delete System Certificate on a mac?

Ok so i'm wondering how to delete a system certificate stored in System Keychain. So i'm a iphone developer and without out knowing the difference between saving in login and system so i choose system. I have duplicate certificates that have been revoked and whenever i try deleting it ask me to confirm and then ask to login with master password and then it says something about being opened in wrong application or something.

Knowing which OS you're in would may have allowed a more specific answer. Check the link below at Apple for advance search option and if that doesn't offer what you are needing perhaps checking with another iPhone developer may help.