Unfurtunately there seems not to be an option to operate on several control's attributes at a time.
I see two ways to obtain what you need:
1. In case you have not yet developed the UIR, change the default text and label attributes in the UIR editor preferences to the font and size you want
2. For existing panels, you can save in text format, make the necessary modifications dorectly in the TUI file and reload the oanels fromt the TUI file. With a few attempts and a smart use of search-and-replace functions of your editor you should be able to solve your problem easily.
Hope this helps
Roberto