You cannot delete keys nor modify UIDs for keys uploaded to PGP key servers.
To change your email, you must add a new UID.
$ gpg --edit-key <keyID> gpg> adduid Real name: <name> Email address: <email> Comment: <comment> Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o You need a passphrase to unlock the secret key for user: "foo <firstname.lastname@example.org>"
Update the trust level of the new UID.
gpg> uid <new uid number> gpg> trust Your decision? 5 Do you really want to set this key to ultimate trust? (y/N) y gpg> uid <new uid number>
Revoke the old UID.
gpg> uid <old uid number> gpg> revuid Really revoke this user ID? (y/N) y Your decision? 4 Enter an optional description; end it with an empty line: <description> Is this okay? (y/N) y
Save the changes. Upload the updated key to your PGP key server.
gpg> save $ gpg --keyserver hkp://pgp.mit.edu --send-keys <keyID>