Through an Accredited Registrar:

If the “.es” domain is managed by an Accredited Registrar, they should be contacted to process the change of administrative contact.
Access our list of Accredited Registrars

Through the Register (Red.es):

If the “.es” domain is not managed by an Accredited Registrar, the holder or administrative contact that appears as registered can request the change of administrative contact.
To request the change you must log onto the domain name management system with your identifier and password, look for the domain in “My domains” section, and select the “Edit domain” option.
 
Keep in mind that, in accordance with the provisions of article Thirteen of the National Plan for Internet Domain Names under the country code “.es”, the data registered for “.es” domains must be accurate and truthful, especially for the administrative contact. Otherwise, red.es can initiate a cancellation procedure of the domain name.
 
*Please note:
You need a digital signature such as the electronic DNI (DNIe) or another issued by any of the following certification authorities: CERES (Fábrica Nacional de Moneda y Timbre), Consejo General de la Abogacía Espanola, Consejo General de la Abogacía Española, Autoridad de Certificación de la Comunidad Valenciana, Camerfirma (Chambers of Commerce), IZENPE (Basque Regional government), Agencia Catalana de Certificación (CatCert), Ecofirma (Ministry of Industry, Energy and Tourism )... [Read more +]