Open up on your vowels when singing your high pitches. This will allow you to have more room for your tones.
Breathe please. Deep breaths and support is everything to give you the support you need during singing. When singing more of a faster song, work on getting quick deep breaths.
Visualize the note or high note when you are singing. I always imagine, smoke coming out of my head when I am singing my very high notes. This helps me to place the note where it belongs making my high pitches more clearer and narrower like smoke coming out of a chimney.
Think even higher on upper tones by giving them breath and support immediately. This will help your pitch and intonation to be more clearer and more open and lovely.
Make sure your jaw is relax. Do not grab your jaw when you are singing. It really kills the tone quality of your voice and makes you go sharp on high notes unnecessarily.