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."
