he's the legal father, but not the biological one

[looking for help in In]

I am residing in Indiana. I have a four year old child. When he was born his biological father di not sign his birth certificate. I became engaged a year and a half later. Six months there after, when my child was approaching two years old, the man I was engaged to signed his birthcertificate as his father, since he had raised my son for the past two yeasr, and if anything was to happen to me, I wanted him to be able to legally care for my child with no problems.. We both signed the neccessary paperwork and had my son's last name chnged to his last name. One and a half years later we ended our ngagement and after abotu nine months of debating on what he wanted to do, the man I was engaged to has decided that he does not want to be legally, or finacially responsible for my son an longer. His biological father, who came back into the picture two years ago, but agreede to abide by what ever I decided about the situation would like to give his son his last name.

Is there a way to have peternity "switched"?
If there is not a way, is the man who signed his birth certificate legally responsible to take care of him finacially even though, he is not his biological child?
Can we just have his legal father give him up for adoption to his biological father?