How do I fix this?
W: The repository 'https://packages.elementary.io/appcenter xenial Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. E: Failed to fetch https://packages.elementary.io/appcenter/dists/xenial/xenial/binary-amd64/Packages Protocol "http" not supported or disabled in libcurl E: Some index files failed to download. They have been ignored, or old ones used instead.