You can use pub uploader [options] {add/remove} <email>
.
Once the new uploader added, you can remove yourself.
pub uploader add <new-owner-email>
pub uploader remove <old-owner-email>
$ pub uploader -h
Manage uploaders for a package on pub.dartlang.org.
Usage: pub uploader [options] {add/remove} <email>
-h, --help Print usage information for this command.
--server The package server on which the package is hosted.
(defaults to "https://pub.dartlang.org")
--package The package whose uploaders will be modified.
(defaults to the current package)