I am getting married in a couple months, and I have an older daughter who has my last name, and I really want her to have my fiancés, and don't want her to have something different than me. So I was wondering how I go about changing it. Thanks.

If she's under 18, you just file at your court house after your marriage.
I hope you have discussed it with her. If she loves her father, your remarriage is hard enough without this. And it won't change her birth certificate.
I think you will find that most children these days keep their original surnames, and are happier for it.

This is a legal issue and has been moved from the Children forum.

Changing a child's name legally requires a court order. It would also require the father's approval.

The thing is, is that she has my last name from when I was born. I have never been married, and she's not biologically my fiancés. she doesn't know that. She's 7, he's been gone for 7 yrs, He's not on the birth certificate. I have custody.