Can't delete old passwords in Keychain Access
I have used various username and passwords to log in to a particular website (makemusic.com) for many years. I have entries in the keychain for web form passwords going back to 2006. I just reset my password at makemusic.com and it generated another keychain item. I would like to delete the older ones so I don't get confused the next time I want to login. I can select the items in question, but when I right-click delete or use the edit menu delete it does nothing. The item remains in the keychain. How do I go about getting rid of these?
Mac mini 2018 or later