My son is 7 years old. He hasn't seen or heard from his father in almost 2 years. He has been asking me and my family if he can change his last name to my last name. How do I go about doing this? What does it involve? What are the costs?

A lot will depend on where you live. In some places you will have to get the bio fathers permission, esp if he has his name and he is on the birth certificate, in other states you may not. Even what court does it, will differ by state, here it is the probate court, but will be one of the county courts in the US.

First stop the county clerks office and see what your state requires , here it is merely a form that is filled out, notorised and filed at court, cost a few hundred dollars.