That is impossible to say because we don't know you, or what your relationship with this girl is like. There is no "one-size-fits-all" way of telling somebody you like them.HotFezz8 said:taking the people who have responded with "talk", where and how would you do it? pub or park? try to kiss her at some point or just talk? etc..
I don't suggest trying to kiss anybody unless you are almost/definitely certain that they'd want you to, and it doesn't seem like she is aware of your feelings for her so that could go horribly wrong.
Perhaps try sitting down with her and telling her? Or when you are out together sometime ask her out on a date or something? Honestly, there is no real way that any of us can say what you "should" do for the reasons I said before, the best we can do is offer a few suggestions.