GPG/GnuPG

Generating new key

gpg --gen-key

List of existing keys

gpg --list-keys

Changing E-mail

For changing mail address should add new uid :

gpg> gpg --edit-key user-id
gpg> adduid
gpg> uid <new uid number>
gpg> trust

Deleting a uid

gpg> uid <uid number>
gpg> deluid <uid>

Saving changes

gpg> save

Deleting key
You should delete secrect key befor deleting a key:

gpg --delete-secret-key <key>
gpg --delete-key <key>

Read more http://www.gnupg.org/documentation/index.html