The final return should have the word "Deceased," the decedent's name, and the date of death written across the top of the return. Generally, the person who is filing a return for a decedent and claiming a refund must file IRS form 1310 - Statement of Person Claiming Refund Due a Deceased Taxpayer, with the return - http://www.irs.gov/pub/irs-pdf/f1310.pdf.
If no personal representative has been appointed by court and there is no surviving spouse, the person in charge of the decedent's property must file and sign the return as "personal representative."
You may be require to file IRS form 1041 - http://www.irs.gov/pub/irs-pdf/f1041.pdf. Please see instructions for filing requirements - http://www.irs.gov/pub/irs-pdf/i1041.pdf