First off, never try to force out higher notes. If your throat hurts, STOP. It is possible to damage your voice por 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 tu can increase your range is to start canto any note, sliding down to the lowest note tu can (comfortably) sing, and then sliding back up to the highest note tu can (comfortably) sing. Another way I like to increase my range is canto a song that has a note just out of my range and make it my goal to hit it.
Also, if tu don't have/know how to play paino to do scales, tu can find videos on YouTube (and other sites) that have the scales tu can practice off of. o if tu don't know how to play the scales, those can also easily be found online and aren't hard to pick up on.
