In some countries, you can change your surname whenever (and to whatever) you like with relative ease, but the rules on surname change are strict in the Philippines. Under Filippino law, a person’s surname is considered to be fixed, and it can be changed only for good reason and in a court of law.
The Philippines Supreme Court declared that the only grounds for change of name are:
To change your surname in the Philippines, you need a court order from the Regional Trial Court of your municipality or city. You file a petition explaining why you want to change your surname and including all required documents. These include National Bureau of Investigation clearance, police clearance, your baptismal certificate, your birth certificate, school records or employment certificate and valid forms of identification. The court will set a date for a hearing, which anyone can attend (and potentially oppose your change of surname).
If the registered birth certificate of an illegitimate child born in the Philippines after August 3, 1988 shows the mother’s surname, the mother, father, guardian or child (if 18 or over) can file an Affidavit to Use the Surname of the Father with the civil registry office that registered the child’s birth. As well as the Affidavit, a Private Handwritten Instrument or an affidavit of acknowledgement from the father is required. If the child was born abroad, her birth certificate must be annotated by the Philippine Statistics Authority. If you are a mother who wants to change your child's surname to your own, you need to get a court order. However, the Supreme Court has ruled that a child's change of surname may only be granted when she reaches 18 and can make her own decision.
It's not a legal requirement to change your surname when you get married in the Philippines, and a woman who wants to officially take her husband's surname only has to comply with change of status requirements. No court order is required. It makes sense (and saves money) to wait for forms of identification (such as passport and driver's license) to expire, then change the status and surname at the same time as part of the renewal process.