How can I become a low pitch singer to a high pitch singer?

First off, never try to force out higher notes. If your throat hurts, STOP. It is possible to damage your voice by straining your vocal cords.

The easiest way to increase your range is literally just to sing your C scale from Do to Do, and then going to your C# scale, then up to D, and so on until you've reached your range. Other ways you can increase your range is to start singing any note, sliding down to the lowest note you can (comfortably) sing, and then sliding back up to the highest note you can (comfortably) sing. Another way I like to increase my range is singing a song that has a note just out of my range and make it my goal to hit it.

Also, if you don't have/know how to play piano to do scales, you can find videos on YouTube (and other sites) that have the scales you can practice off of. Or if you don't know how to play the scales, those can also easily be found online and aren't hard to pick up on.