Working with your lower register to build some timber into your vocal is key to your singing success. I've seen singers make the same mistake time and time again, they jump straight onto a higher octave from the get-go, thereby limiting their range. To improve your range, use your lower register (your deeper, speaking voice)! One of my main tasks when teaching voice at my studio is to help my students find that missing link. Imagine yourself climbing a flight of stairs and instead of stepping on every single step on the way up, you jump a few as you ascend. When you're not connecting your notes with every step from the ground up, your vocal flow becomes erratic; your vocal range becomes very limited; and you lose that vocal control you could've easily had.