Hello,

For the 2006 and 2007 years I used form 1040EZ and not 1040NR-EZ as I should have done, what should I do now? I'm an international student on F1 visa.

Thank You!

Also, is this the only form that I need to fill (1040NR-EZ) as an international student?

On F1/OPT you are exempt from residency for 5-years. You must file non-resident tax return Form 1040NR or 1040NR-EZ and Form 8843.

Your income is not subject to FICA taxes but you must pay federal and state income taxes. On your OPT income you will get deduction based on tax treaty between the U.S. and your country.
Read: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents

Thank you MukatA !

I have another question...

to file for amend using 1040x for the years 2006 and 2007, can I use 1040NR-EZ from the 2008? Or should it be 1040NR-EZ from 2006 and 2007?

Thanks

How you do it is your choice.
Normally, you should file nonresident return for 2008.

You should file amended tax returns (Form 1040X along with properly done nonresident returns and Form 8843) for 2006 and 2007. You can do it now or whenever you get time. If you owe tax on amended tax return, you must pay with interest and penalty. If you do not owe tax, then you will not pay interest and penalty.
Also if you file amended tax return on your own you can request for waiver of penalty.

When you amend the 2006 return, use the Form 1040NR-EZ for 2006.

The same for 2007 and 2008.