This question gets asked in the Forum a lot. There are over a dozen threads (because NOBODY uses the "Search" function before posting a new one) dedicated to that topic.
To save time, here's the short answer:

YOU DON'T.

You have what you have, and that's the luck of the genetic lottery.
Learn to love it and live with it.
Quit being such a damn baby.

(Of course, you could always borrow a bigger pecker from a well-endowed friend, but loaner cocks don't really count.)