I would talk to your local title company for starters. Call TItle Guaranty in Hawaii Kai and ask them to help you out. You may need a real estate attorney. If so, I can recommend one.
It's not clear how it will work, if you are making the mortgage payments, but your friend is releasing their interest in the property. How are you going to let the mortgage company know that someone else is making payments? I think what you're saying is that you want the other person to be released from the deed, but you are the new mortgagor (making the payments). Anyway, talk to TG or another title company (there is Island Title on Kapahulu).
Frank Diaz (RA), MBA