Always use care when editing the Preferences file.
You can change the font in the Preferences.txt file for Carrara. To do this, browse to the file which should be here:
Users:[User Account]:Library:Preferences:DAZ 3D:Carrara 7:Preferences.txt
In the document, find:
FONT “ “
Change the FONT line to:
Save the file and relaunch Carrara 7.