Change of date of birth with a difference of two years is a major issue. How did this happen? and why was it left for so long? What you do depends on what is your age, education and or if you hold a government job or entering a government job.
Age cut off becomes important for school admissions, Voter's ID, Driving License, college/degree education, eligibility for government job applications and grant of reservation benefits if any.
For instance, if your school admission age while taking X standard exams was 14 years while your real age was 12 years, then you would be ineligible for the class you are/were studying because 14 years is the minimum age to be eligible for taking up X/SSLC/CBSE exams. This logic would be applicable to all other documents that I have listed above.
If you can give us your month and year of birth that is on your government birth certificate and your school documents and if possible mention what you are doing, then we can advise better.
In case the example of 10 yrs declared vs 8 yrs in truth is what you are hinting, and you do not want to disclose more details, meet a good lawyer with all the relevant documents for further proper guidance. I say this because you should not get into further legal hassles. For example, if you have got your Voter Card based on your school certificate age as 18 yrs, while you true age was 16 yrs, then your vote would illegal. Similarly, if you are in a government job wherein the age of entry is 21 years and your actual age was 19 yrs, then again your appointment would be illegal.