To access your Moneydance preferences, choose File > Preferences.

On a Mac, choose Moneydance > Preferences.

This article details the options available within the "Appearance" tab.

ThemeChoose from multiple colour schemes, or select "customize" to create your own.
FontChoose your preferred font from the drop-down list.
Numeric FontAs above, the font that is used for numeric characters.
Printing FontThe font used when printing reports, graphs or cheques.
Font SizeSelect +1, +2 etc to increase the size, and choose -1, -2 etc to reduce from the default font size. 

Using older versions of Moneydance, you'll find the 'Theme' option within 'General' preferences.