How do I get him think of me as more?

So I have this crush on a guy that was friends with my brother for the longest time. We all had sleepovers and play dates when we were kids and my brother and him didn’t talk at all in middle school or the first few years of high school. Now that I go to the same high school as my brothers friend and not my brother I’ve realized he’s kind of the perfect boyfriend. I have a major crush and want to ask him out so badly but I think he thinks of me as a little sister. I need some advice on how to get him to think of me romantically.