Greetings :
I am an F1 student, in the USA... I used the Form 1040-ez and I mailed it... but I discovered that I must use another tax form... what can I do now? Must send the 1040nr-ez file or should I do another thing?.

Best Regards.

You will file amended tax return. For amending your tax return, you must file IRS Form 1040-X with properly done nonresident tax return Form 1040NR or 1040NR-EZ and Form 8843.

Column A is what was on the original return, Column C is what should have been there (that is corrected amounts) and Column B is the difference. Complete these columns and then refigure your tax. If you owe tax, write check to United States Treasury and enclose with the amended return.
Read: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents (http://taxipay.blogspot.com/2008/03/us-tax-filing-requirements-for-non.html)