How can I get a model body?

I'm 5'11and 148 pounds and 16. I want more of a models body. I'm slim but I'm still not happy.I can wear a small in some shirts but I pick more of the medium or large. I'm like a size 9 in pants and shorts but my shorts are getting kinda big for me. I'm a 34b and I want to be about a size 5 or 4 if that's possible.
How can I get a model body?
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