Have you kissed her? That's the honest to God only way to tell if there's some sexual chemistry. Let people down vote me for saying it but it's true. I'm going to proceed to tell you how I believe you should proceed if you want to succeed in making this girl a romantic partner, but before I do I have to tell you something more important.
She MAY never reciprocate your feelings. It will hurt and you will be disappointed, but life is not going to end. You WILL be OK. You WILL be a better person for putting yourself out there and being vulnerable. It will take time to process and heal but you will rise like a phoenix from the ashes, stronger than you were before, ready to woo the next hottie you set your sights on. That is a fact. Recocgizing this and accepting it is how you "not give a fuck".
First step, just chill out. Sometimes the best things in life take a little time. You've already been her friend for four years, I guarantee you that another day or two won't kill you. Seriously, you have to make sure you don't come off as needy or impatient, most women find that unattractive. The more you "need" her, the less she's going to want to fuck you.
Second step, make casual plans to hang out with her. It doesn't have to be a "date", but make sure it's just the two of you. You've been hanging out with her for four years, you obviously get along and enjoy each other's company on some level. Just approach the situation as if nothing awkward ever happened and you guys are hanging out like you did before.
Third step, tell how she makes you feel. This is the most important step and needs to be done in the right way. At some point when you are hanging out, ideally right after you just made her laugh or you two are having a good time, grab her by the hand (not forcefully, but gently and deliberately) and look her directly in the eyes. Say "I have something important I'd like to tell you" while maintaining eye contact. Pause and briefly look at her lips and then back to here eyes. Proceed to tell her how she makes you feel. Don't say, "I like you". Tell her how she really makes you feel. This is something you should think about beforehand. Examples include: "you make me the happiest man in the world, when I'm with you I don't have a care in the world except seeing you smile", "you make me feel like no other woman has in my life, you make me want to be the best version of myself I can be because you inspire me", "when you laugh I feel like there is no wrong in the world, your smile is the light that brightens my life". These may sound corny but they are just examples. You need to sit down and think about all the good feelings this woman evokes in you. Tell her that. Evaluate her facial expressions as you are telling her these things. Anything but a frown or reluctance to make eye contact or a seizure is good. (VERY IMPORTANT: At some point tell her that you will be OK if she doesn't reciprocate your feelings. Her feelings about you do not change your feelings about her. You want her to want you but more importantly you want her to be happy, and if that means not with you romantically then that is OK) Briefly pause. If she is presenting negative body language, it's best not to proceed to step four or it will most likely end poorly.
Fourth step, tell her as you look her in the eyes, "there is nothing I would rather do in this moment than ______ (insert: kiss you or be with you). Briefly pause. Look at her lips then back at her eyes as you move your face slowly towards her face. Kiss her.
This is not an exact science but a general progression. It doesn't need to be verbatim but should follow the themes presented above. Here is an example of how this could go down: "[girls name], I have something important I'd like to tell you. I love your company. We've been friends for four years, four amazing years and our friendship means the world to me, but I can't help but feel like there's something more here. Whenever I'm with you, you make me feel effortlessly happy. Your laugh is music to my ears. You inspire me by just being who you are. I know we've kind of danced around this before, but I have to be true to myself and tell you how I feel. I want to make you smile. I want to make you laugh. I want to hold you when you're down. I want to make you feel like you're the most important girl in the world, the only girl in the world because you make me feel like no other girl has ever made me feel. If that's not something that could see yourself being a part of, then I'll understand. I just want you to be happy, because you make me so happy. With that being said, right now, in this moment, there's nothing I'd like more in the world than to kiss you." Proceed to kiss her.
This is just my 2 cents. I'm no pick up artist but I have had success with this general formula of just expressing my true feelings and going for it. The key is sincerity and confidence. If she isn't into it then it wasn't meant to be.