I am not able to raise the water level inside the tank. I tried turning the adjustment screw on the fill valve clockwise but the level stays the same.

Try turning it counter clockwise.

Is this your model? If so the adjustmet is at about the 7:40mark.

https://www.youtube.com/watch?v=lbU80u1mpUM

Or this second video may be more helpful.

https://www.youtube.com/watch?v=R6ollyL8bk0