Long tones are one of the major keys to your success.  This will develope your mouth muscles, your diaphram, and your mind to horn tone interaction. Do it with a metranome and also do it against a wall to hear your tone better. You may also do it in front of a mirror to make sure you are keeping a good hand position as you get familiar with the larger horn.I myself made the swith in 8th grade, and had a great instructor that demanded I followed through and got control of the larger horn.