I don't have great range, but I've just become comfortable exploring high C and the notes just above in a relaxed melodic way. This new experience for me has involved in chronological order, increasing and regularizing my playing time to at least 45 min almost every day. Switching from Bach 7c mouthpiece to a Schilke 14A4a. Working the pencil holding exercise found on youtube. As mentioned here, spending at least as much time in the lower register as the upper, with long tones and slurs. Letting go of "note" as a concept and concentrating on "sound". Playing Baritone horn and Bass trumpet with a larger mouthpiece! I have found that doubling on the lower brass has strengthened the outer muscles of my trumpet embouchure and made a quantum synergistic improvement in both tone and range for both instruments. This has been groundbreaking for me!