To delete a repository, open “/etc/apt/sources.list” file:
# vim /etc/apt/sources.list
To delete a repository, remove the entry, Save and close the file.
If you have added PPA repositories, look into:
“/etc/apt/sources.list.d/” directory and delete the entry.
To delete a repository key, use “apt-key“
First list all the repository keys:
# apt-key list
Then delete the key:
# apt-key del “1111 2222 3333 4444 5555 ….”