Increasing your range takes time and intention. Just like you don’t just do the splits overnight. It’s a process. You have to be intentional to stretch certain muscles consistently to increase your flexibility. It’s the same range with stretching your vocal range. Don’t push it. Just do a little bit more each time and rest.
Always warm up your full voice meaning low notes to your highest notes. Most people think of increasing your vocal range by hitting higher notes. However, increasing your range also means increasing your lower notes. Some students tend to avoid high notes and some tend to avoid the low notes. It’s important to warm up both.
For higher notes, you need less air and you want to try doing lots of Sirens, Sighs or Yawns to lift your soft palate and create space in your throat because the tendency is to feel constriction on the high notes. For lower notes, you need more air. Sing the notes as if you’re fogging up a mirror. If you need specific exercises, I have more extensive warm ups in my Sing Online Course. Purchase now at 95% off here: https://www.joanncchang.com/you-can-sing-today-course/