Me and my partner are about to start a family. What paperwork do I need the sperm donor to sign in regards to his relinquishment of parental rights and where do I get it?

Did you read this? https://www.askmehelpdesk.com/family-law/signing-over-rights-read-first-116098.html

I would also be careful with your "sperm donor" comments - the Court does NOT look lightly upon such comments and they make you look bad.

If you had a sperm donor, they don't have rights. They actually give them up when they donate the sperm at the agency.

Oh--you meant the guy you had sex with and no longer like! Well, he's not a sperm donor--he's a biological father.

You and your partner--MARRIED partner? Most states have marriage as a pre-requisite for step-parent adoption. If it's a same-sex partner, you really need to check the laws in your state--some states don't allow it.

Finally--get a lawyer. You CAN go through an adoption without one, but you can also set your own bones without a doctor as well. If you want it done RIGHT, with no chance that it could ever be overturned, then you need a lawyer.