My husband had in ITIN last year, as of Aug he has SSN I was informd of a form he can file with tax return. How do I go by doing so? or do I have to do it at an office?

Here, from a SuperUser (@bine22) are instructions on how to proceed when you used to have an ITIN and get a SSN. Make sure to select "See entire answer":

https://ttlc.intuit.com/replies/4319430

Some additional comments on e-filing:

According to the IRS.gov website, you should put 0 for his AGI.

 From the IRS website below.

"Question: If the taxpayer had an ITIN (IRS Individual Taxpayer Identification Number) when they filed their 2013 tax return, but now have a SSN this filing season (TY2014), what Prior Year AGI amount should be used?

Answer: If the taxpayer had ITIN when they filed their 2013 tax return, but now have an SSN to file their 2014 tax return, they should use “0” (zero) as the Prior Year AGI amount."