you should import a new font and then in import settings you can change the size of your font. search google for "free ttf fonts" and you will find many fonts on the net. i think there are some fonts in standard assets too.

increasing font size is simple. first find the font in the project view, select it then on the font texture, change the size, and to reduce edge pixelation, make the font size larger and the object smaller (if possible)