You can get the form2 (renewal / re-issue) downloaded from the Govt Of India website – http://passport.nic.in/ , fill it and submit it in person with all enclosures either at regional passport office at Shastri Bhavan or at local police stations (they accept at Annanagar K4 police station). The fee is accepted in cash at regional office while only DD is accepted at other offices. Better go for Tatkal (few weeks) as it takes 4-5 months otherwise (the fee is slightly higher for tatkal ).
You need to provide proof of address (if address has changed) and marriage certificate (or affidavit from rotary public on 20Rs stamp paper) if married and want to include the name of the spouse (mandatory and recommended if married). All signatures in the form will have to be signed only in person in front of the officials while presenting the form.
All details are mentioned in the FAQs (check for applying for kids also) at the website as well.
Going through agents (will charge 3k to 5k) isnâ€™t worth the money!
For online application: