Are you talking about the dialogue boxes that appear that guide you through distributing your PDFs or the default text formats of text fields?
Im afraid there is no way to change the dialogue box, at least not from inside of Acrobat. Possibly could by messing about with system folder, but would not recommend.
However, if its the text field formats, change it to your nex font and choose the size, then click close, then ctrl click/right click over the field and choose "Use current propeties as new defaults"
Hope this helps?