To actually be able to sing better and louder? Well, the easiest answer would be to take a singing class. Basically what they do is extend your range (by practice of the do re mi scale) until you can sing higher, and at the same time louder. Singing BETTER… Well… Natural talent? Singing classes might help…
If you don't want to pay for a class, just search up vocal exercises and practice them regularly; try to go right out of your range, but not too far otherwise your voice will crack.

Okay I'm gonna try to help you here lol.

When it comes to singing there are 4 main pillars that every singer must understand and be able to do to have a good voice and they are

1.Breathing: Lie flat on your back with a book on your belly and try to get the book to raise. When you have got the hang of that try doing it standing up its a bit harder lol.

2. Support: Take a proper breath and sustain a ZZZ. Notice how there is a slight tension in your back muscles. This is a good tension your basically preventing the ribs from collapsing. Therefore your using less air to sing. Less air =Less Effort and better Tone 😀

3.Placement: This one is hard to teach Its commonly referred to has singing into the mask. So Google it and you will find some good Videos on it and stuff.

4.Emotion: And for this one you just have to really feel the song imagine that you wrote the lyrics and that you are really passionate about them

I know you said don't recommend any teachers but you should check out jamie venderas raise your voice book lol its only like 20 dollars and its really good. Hes the guy who broke a wine glass with his voice alone on mythbusters.

Srry if this didnt help!

Yeah you can buy this "teach yourself to sing" book at any music store…itll help you out alot…remember ANYONE can sing…notice how you sing good(or better than usual) in your car or shower by yourself?? Thats cuz your relaxed…always remember to relax…sing by yourself as much as possible to songs you know is the best practice…dont play the music loud or you wont be able to hear your own voice and make adjustments on your pitch|tone…after a while youll be able to sing those songs without the music playin..i used to sit in my closet with my stereo and sing alot for hours everyday(no lie)…and it worked out very well…good luck.