Play long tones to increase your high range. Start on an F concert in the middle of the staff. Move up to an F# and then move back to F. Continue to do this, adding a half-step each time until you are playing F - Bb - F.
Play long tones an octave higher starting in the F concert at the top of the staff. Continue with the same series from Step 1. Go as high as you are able to without removing the mouthpiece from your lips. Resetting the lips is a form of cheating and will not help you develop your embouchure.
Take a 10-minute break and then repeat Step 2 to see if you can go any higher. If you do not know the fingerings for notes above high C, view the resource in this article.
Stop practicing after playing the second set of exercises. You can continue to practice, but don't attempt this exercise again until the next day. Too much practicing will actually hurt your embouchure.