All registered aliens and ACR I-Card holders, except Temporary Visitor’s Visa holders or Tourist Visa holders, should report themselves each year in the first three months of the year.
Reporting must be done at a Bureau of Immigration (BI) authorized office, or what they call field offices. Make sure you are decently dressed, e.g. long pants or dress, shoes (no flip flop's) and shoulders covered. when you go there.
A list of offices and the services they deliver can be found here.
The fee is 310 pesos. If late there is a penalty fee.
I did my reporting already in January 2015 and used the old paper form application. The form is available in the office. The whole procedure took me 30 minutes. Don't forget to bring your ACR, passport and payment slip of last year's reporting.
BI has developed an online reporting application website, see here. As far as I know it is not yet a requirement to do the registration online, see my experience above. But, if you do then print a copy of the application form, including the CONFIRMATION NUMBER, and bring it also with you when you go to the BI office.