How can I renew Philippine passport if my old passport didn't have a midle name yet I later ifound out my real birth certificate registered at NSO that has a midle name on it,and that's why I wanted to renew my passport! please help me for this folks!thank you,

You wish to correct your name, are you currently in country, or outside country? when does passport expire.

And why is it so important to add middle name ?

I think you might have to contact the following people to get the information in your passport modified.

DFA Consular Office:
ASEANA Business Park,
Bradco Avenue corner Macapagal Boulevard,
Paranaque City
737-1000

Source : Philippines - Modify or Change Information in Passport - Wikiprocedure