Short answer. In the trial court of the province where you reside, and you must have been a bona fide resident of that province for at least three years before filing. This judicial route applies to changes such as a surname; a first name or nickname change generally goes through the administrative process instead.
What the law says
A person desiring to change his name shall present the petition to the Court of First Instance of the province in which he resides, or, in the City of Manila, to the Juvenile and Domestic Relations Court.
Rule 103, Section 1 — Venue. Read the full provision →
What the law says
That the petitioner has been a bona fide resident of the province where the petition is filed for at least three years prior to the date of such filing
Rule 103, Section 2 — Contents of petition. Read the full provision →
Venue is tied to the province of residence
The petition is filed in the trial court of the province in which he resides. The names of the courts in the rule's original text — the Court of First Instance and the Juvenile and Domestic Relations Court in Manila — reflect the court structure before the 1980 Judiciary Reorganization Act; petitions of this kind are now filed with the Regional Trial Court of the petitioner's province of residence.
Three years of bona fide residence is required before filing
The petition must set forth that the petitioner has been a bona fide resident of the province where the petition is filed for at least three years prior to the date of such filing. This is a real, substantive requirement, not a formality — a petitioner who recently moved to the province cannot yet meet it, no matter how straightforward the underlying reason for the name change.
This judicial route is not the only way to change a name
A court petition is no longer the sole avenue for changing a name. RA 9048, as amended by RA 10172, created an administrative process before the local civil registrar for changing a first name or nickname, and for correcting clerical or typographical errors — no court case required at all for those specific changes. The judicial petition described here remains the route for changes the administrative process does not cover, such as a change of surname.
Why identifying the right route matters
Filing a judicial petition for a change the administrative process already covers wastes time and money on a court case that was never necessary. Anyone considering a name change should first determine whether what they want falls within RA 9048's administrative scope or genuinely requires this judicial petition, since the venue and three-year residency requirements above apply only to the judicial route described here.