I have been with my husband now for 2 years (legally married just recently). I have a 5 year old son from a previous relationship (never married). My husband wants to legally adopt my son and I know that my son's biological father has to relinquish his paternal rights. My questions are: do I have to contact him and ask him to do this or can I go through the courts? Is there a specific form the biological father needs to sign before we go to court? And being that my husband now wants to adopt my son, would that relieve the biological father from paying child support?

You have to contact him. You can't force him to relinquish he has to voluntarily do it. Get an attorney to draw up the paper and send it to him to sign.

The adoption would relieve him of support commitment, though relinquishing by itself won't. So doing so is to his advantage.

As noted your attorney draws up the paper work, it is sent to him and he signs it and it is filed with the court.

If you are on good terms with him, you may wish to call and discuss this with him, since if he refuses to sign them over it may save you a lot of time and trouble