As you sing up to higher notes, you want to focus on compression and resonance. You need to have gradations of compression to smooth out the mix. Keep the air the same as you move up through the mix. Finally, make the air stay in the head like its falsetto, but keep compression on the vocal cords.
When you go up in pitch, don't push the breath and spread out. You're also not going to flip to falsetto or head voice. Keep it in a light, compressed, easy mix.