In order to increase the angular magnification of a simple...

The angular magnification of a simple microscope is given by $M = 1 + \dfrac{D}{f}$ or $M = \dfrac{D}{f}$, where $D$ is the least distance of distinct vision and $f$ is the focal length of the lens.

To increase the angular magnification, the focal length $f$ must be decreased.

Since the power of a lens is given by $P = \dfrac{1}{f}$, decreasing the focal length is equivalent to increasing the power of the lens.

Therefore, to increase the angular magnification, one must increase the power of the lens.