The first thing you have to do is develop the muscles inside the larynx so that when you sing any given pitch the muscles inside the larynx have the strength, flexibility and conditioning they need to work without the help of any outer muscles.
You do this by increments. The first thing you have to do is accept that your intrinsic muscles (the inner muscles of the larynx) are not developed yet to sing the pitches your desire (those loud high notes) without the help of the outer muscles. So you start at point one and develop them from there. Point one means a light and easy voice that does not require the help of any of the outer muscles. To make sure that they're not helping you out look at yourself in the mirror when you vocalize and make sure that not a single muscles on your face and/or neck is showing any activity. When you make sound this way it means that the intrinsic muscles are doing the work, instead of your face, neck, jaw or tongue muscles. By the way, the tongue can be trickier to monitor so vocalizing with a finger in your mouth on a single vowel slide and making sure that the tongue is not moving at all (the tongue should not be involved in the pitch creation process... it is an outer muscle that should only be used for vowel and consonant shaping).
When you let go of all your external muscles you will feel that you have no control over the voice, because you are so accustomed to using them that you'll feel at a loss when you let them go.
Only when your outer muscles are relaxed are your intrinsic muscles doing the work (which makes them become stronger, more flexible and conditioned to work independently) and are you on the road to vocal freedom.
You have to be able to put the quality of sound in the back-burner and give sole priority to muscular independence and efficiency. Whenever you are using your face, neck, tongue or jaw muscles to produce sound you are making those muscles stronger! The vocal folds are very very small and if you want to make them stronger you have to make sure that they are working independently.
If you vocalize with muscle efficiency in mind instead of sound you intrinsic muscles will become a lot stronger and more flexible and your voice will be conditioned to work more efficiently. Vocalizing is a million times more effective than singing songs for improving the voice because you don't have to focus on words, emotion, phrasing or performance. In vocalizing you're building your skills and in singing you are using your skills. The more built your skills, the better your singing. So building your skills first is the way to go!
If you want to learn more about this, there are many excellent books out there that you can read. But I would recommend that you start with a simple one and as you learn read other more technical ones. Start out with "The Rock-and-Roll Singer's Survival Manual" by Mark Baxter. It will help you a lot.
Remember, it takes time to build your voice. I hope this helps.