According to user Scott D Davis on the Autodesk Revit Architecture Discussion Group forum, to find the configuration settings, user Scott D Davis said:
"You must open the Revit.ini file, which is located in the Revit Program folder. Edit the Revit.ini in notepad, and add the line TempDimFontSizeInPoints=16 (or whatever point size you would like) under the [Graphics] heading in the file, and save it. Then re-launch Revit. This is for Revit 2010 and earlier. In Revit 2011, this will be handled in the Options located by clicking on the Application button at the top left of the Revit window. (The Big type "R")"