How to delete ONE text conversation thats over 2GB? (IPhone)?

My girlfriend and I have been dating for a year and I haven't deleted them since. They've now accumulated to over 2GB. How can I get rid of them all?

When you click on the message app, find your girlfriend's texts. Don't click on the message to open, but swipe left and there will be a delete button that pops up and you hit that. Or another method is when you click on the messages app, you can click on "edit" in the top left corner, click on your girlfriend's text and then hit delete. Once you delete the conversation it might take a few moments to clear since it's using so much space.