Help me change my name

My legal name is Kennedy. I was named after my maternal (step) great grandfather who stepped up and helped raise my mom after her parents divorced. But he named me Sam. After 13 years of being Sam Kennedy to everyone we know I asked my parents if I could make my name Sam Kennedy for real.  They agreed and it put my Pawpaw in tears to know that I have chooses to legally take the name he gave me.  He's 88, a Korean War vet, and a cancer survivor. But most importantly he's my Pawpaw.  We know he doesn't have much time left and we all would like him to be with us when we change it.  So I'm reaching out to the great people of the internet to help me dream of being Sam Kennedy come true.