Wondering what I have to do to get a paternity test done. We have been divorced for over ten years and I have been paying support. I found some info that the child is not mine and I want to get to the bottom of this. Please help me

You have to have one appointed by a judge. So basically if you are legal illiterate I would suggest going to an attorney and explaining what you want to do so that he can send the proper documents to the courts for your request. It is illegal to give legal advice unless you are an attorney so that's where I would head.

Do I have to get a lawyer or can I do this on my own

If they are going after you for Child Support the best way to do it is to go through the Child Support court and they might give you a court appointed lawyer if you qualify.
If it is about getting your name on the birth certificate don't sign anything until the test comes back.