Repay tax

[prem85]

HI,

I am working as a Postdoc since Jan 2014. I claimed tax exemption for FY2014. Thereafter I decided to stay longer in US and around mid 2015, I asked my employer to deduct Federal and State taxes.

Now I would like to know how to return the original tax for year FY-2014 and 2015. Does IRS ask for interest? And is it possible to pay it in installments???

thanks