git remote rename original6 newname
Should be the command you're looking for. This will allow you to rename the old remote to something else and add a new remote named original6.
If you want to delete the remote, type:
git config -e
And manually delete the listing from your config file.
There should be an entry that looks like this:
[remote "original6"]
url = somebody@somewhere.com:something.git
fetch = +refs/heads/......
If you delete those lines from your config, you should be good to go.