Changing passport from Natural born name to adoptive name

Good evening to all...

I am a 50+ year old Filipina, widowed for 5 years now.

I am seeking legal advice in regards to my name. I was adopted legally and thus the change of middle name and surname. My first name was retained.

When I applied for a passport in 1997, the travel agent was not able to secure a birth certificate under my adoptive name. Since I was in a rush, we decided to use my natural born name and that's the name I used when I went abroad.

Now that I'm back here I've been using my adoptive name again.

My question Sir/Ma'am is... what shall I do in order to get a passport under my adoptive name? I have all my other identification cards under my adoptive name, even my school records are under my adoptive name as well and I also got married bearing my adoptive name.

I am planning to go abroad soon but I am not certain what should I do.

Your assistance is highly appreciated.

Thanks and best regards,