Relax your whole body so that your muscles are loose and flexible enough for movement. Tension in your body will make it difficult to relax your vocal cords enough to produce quality sounds. Stretch and breathe deeply for a few minutes prior to singing.
Perform vocal warmup exercises before you sing. Gentle warmup exercises allow for increased blood circulation, which promotes elasticity and enables vocal muscles to handle the dynamic activity of singing. A simple warmup session might include humming, lip trills and scales.
Support every note with your diaphragm, which is located 2 inches above your bellybutton. If you begin to notice tension in your throat while singing, it is likely that you are not supporting your voice with your diaphragm. Stop singing immediately if you feel tension as it is possible to damage your vocal cords if you sing incorrectly.
Maintain good posture while singing. Your neck and back should be straight and your rib cage should be expanded for optimal oxygen accessibility. Good posture will also help your diaphragm to function properly.
Do vocal exercises to increase power in your range. Head voice octave slides are exercises where you sing scales starting from your chest voice and escalating into your head voice, going up a key after each scale. It is important to relax your cords as much as possible during these exercises and focus on shifting to your higher register. Be gentle with your vocal cords doing these exercises and don't push the higher sounds out, but instead focus on relaxing the muscles of the larynx enough to allow the higher notes to flow freely.
Practice consistently a few times a week to achieve a more powerful and higher range.