Hi, -In may 2015, one of my band directors (a retired trumpet player) told me that i was playing with a too low embouchure placement, and that my lips were very very stretched, allowing me to have a great upper register.My top lip was dominating the low lip in the mouthpiece (i had kind of an overbite) so it made me play on the red of the upper lip. But this setting allowed me to have a great sound and a decent upper register ( i could reach a high C at 14 years old).The thing was that my endurance was limited. So my teacher told me to change the setting that I had to a centered, relaxed, standard placement that would allow me to play higher, better endurance and better control. I kinda started to try some things but I gave up. -September 2015 to now : I began the embouchure change. I started gradually, just by placing a little to the center. Great still could play to a high B. Tossed it to the centerest position i felt and boom. I couldn't reach an F third line and even my low register was awful. I thought that it was part of the change, spoke to my private teacher about this, she told me to take days off the horn which I did. When I came back, I did some long tone drills in the lower register, it worked. I just could reach a high G. Practiced some Clarke, flexibilities and the high A then B flat (occasionnaly)came out. I am stuck here since December. I put too much pressure on my lips. Put less pressure more air, nothing's changed. When I free buzz it is dispersed on many areas of my lips and my left lip corner is not as relaxed as the right one. When I play, the left part of my inside cheek skin goes between my teeth and when I want to go higher than a high B flat, my aperture just doesnt want to go smaller, the buzz stops but i can still hear the air making a high C. I watched many beginner tutorials on embouchure, nope still nothing. I wanted to make a career out of music, which I love, and I don't want to quit playing this beautiful instrument. If anybody can help, it could make me happy for the rest of my life. Sincerely. A desperate passionate player. NB: Now I play centered 1/2 and 1/2 placement, slightly to the left.