GNOME Tweak Tool is a tool that can be used to change the fonts and other UI elements of GNOME. Since Ubuntu Unity is based on GNOME, this affects how many of your applications and desktop will look.
Installing the tool is easy:
$ sudo apt install gnome-tweak-tool
It can be invoked from the Dash as Tweak Tool or from the shell as
I typically use this tool to change the fonts for the Window Titles, Interface and Documents. These apply to an astonishing array of UI elements in many applications that are built on GTK or GNOME.
Tried with: GNOME Tweak Tool 3.10.1-2 and Ubuntu 14.04