How can I notify an address change?

My NIE renewal application was submitted through Registro Interno Oficina de Extranjeros en Barcelona last month, and I was told the approval notice would be mailed about 1.5 months later to the address typed on my application form. But afterwards I decided to move to another flat later this month. How can I notify the agency of an address change? Is it possible to get it done online? Any advice is appreciated.