I am from Houston, so please enlighten me more.
I understand the appearance aspect of it but what changes should I make personally, like the way I walk, talk, act, the things I do, how I should have my body, things of that nature
Just act natural. Distance yourself from any "urban" manner of speech; you want to speak "correctly", you don't want to sound like some 5th Ward thug.
This would be easier if you were from Dallas, but: just imagine that you've grown up in River Oaks ("Rivah Ooaks" as the rich old ladies would say), had servants, Daddy taking you to "the box" at Reliant and Minute Maid (oh, you love baseball, too, but you're not all that wild about basketball), Mom running you over to the Galleria to buy you some clothes. You've had the life of luxury, with people waiting on you all your life.
While you're nice to everyone (it's a rule), and polite to a fault, you must remember that you are the child of captains of industry and commerce and medicine and the law, and one day you'll be one, too. As such, you're just a little better than they are---and that's the whole essence of it. The true New England prep (I lived in NYC and met plenty of J. Wentington Farquar IV types) is a bit more snobby than the Texas variety, but the Texas variety is just a bit more subtle. You don't quite say "my good man" when you say, "Thank you" to the waiter, but it's implied.
Kind of hard to put into words. Practice.
(to me, I'd rather you'd just be yourself and let the rest take care of itself. Being genuine is actually the mark of a true gentleman; the clothes are just an expression of that---plain, cotton, wool, leather, comfortable, durable---you're better off just being you. But that's my opinion).