I am an F1 student in USA for last 3 years. The first year (2007) I filed 1040 NR EZ. For 2008 I used turbotax and filed 1040A which I realized to be a mistake later. Now I filed 1040 NR EZ for 2009 last week. Now how do I amend my last year's returns?
Also I worked for a few months last year where social security tax was deducted from my pay, should I pay this tax? If no, how can I try for a refund of this amount, I already filed my 2009 returns and did not mention anywhere in my return about my social security tax.
Thanks.

For 2008 file amended tax return with property done nonresident tax return and Form 8843.
For 2009, you were also required to file Form 8843. Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents

To get SS tax back, you need to file Form 843. File only after you have file amended tax return for 2008 and wait for about 8 weeks.
Your U.S. Tax Return: Social Security and Medicare (FICA) Taxes for Non-resident Exempt Individual

Thank you MukatA for your response.
I did file 8843 for 2009.
Should I also file my amended tax returns for 2008 before April 15?
Thanks much.

It is not required that you file amended tax on or before April 15. If you owe tax, file soon.
Still it is better to file without delay.

Thank you MukatA for your response.
I have one more question.
I file IT 140 for my state returns (west virginia), What should I fill in the federal adjusted gross income? Is it my complete Wages and salaries (line 3 of 1040 NR-EZ) or my wages after deducting the standard deductions?
Thank you so much

AGI for you would be Line #3 of Form 1040NR-EZ.