Non submission of pension income to employer

I have not declared pension as income to my present employer for FY-2012-2013. And while computing salary of my present employer the total income does not attract income tax and accumulated pension for the year too will not attract any tax but calculating pension along with definitely attract income tax. I want to pay income tax now. How to pay income tax and file ITR within 31 st July 2013? I have not filed ITR for preceding years.