Will it be easy to terminate the parental rights of my ex? How?

My son's father (my ex-husband) still has parental rights, however he has not been involved in my son's life for many years. My current husband wishes to adopt and change our son's last name to his/ours, but first we must get my ex-husband’s rights taken away. Ex refuses to sign them over despite being asked a few times in the past. I now do not know where he is or how to contact him. In our divorce decree, it is stated that he gets no visitation rights as it's not in the best interest of the child, so he has not had actual visitations, though a few times through the years I have allowed him to visit our son, but it hasn't been in the past year or two. He does not pay child support minus one and a half payments that were withheld from a paycheck (I presume as I have not seen a dime in the past 7 years until then) about 6 months or so ago. They abruptly stopped after that. 7 years ago we did go through the courts not just for the divorce, but also for domestic violence and dealing with CPS, and he never finished the 'Plan' they made for him, which included parenting classes, weekly counseling and BIP. How do I go about getting his parental rights terminated in this situation? If I received those child support payments in the past year, would that keep me from being able to go to court without him to get his rights terminated, even though he hasn't seen our son in over a year? Would I be able to change my son's last name before getting my ex's parental rights terminated? (He's now almost 8 and we would like to change his last name before he gets any older)