14 CFR 47.45: Change of address.

Within 30 days after any change in a registered owner's mailing address, the registered owner must notify the Registry in writing of the change of address. If a post office box or mailing drop is used for mailing purposes, the registered owner also must provide that owner's physical address or location. Upon acceptance, the Registry will issue, without charge, a revised Certificate of Aircraft Registration reflecting the new mailing address. When a post office box or mailing drop is used for mailing purposes, and the registered owner's physical address or location changes, the registered owner must notify the Registry in writing of the new address or location within 30 days.