As a newbie, I was quite confused by all this. My situation was that I was placing door and window ID symbols in a drawing - the window symbols were basically fine, but the door sybols were messed up. The circle was the right size, but the text was way too small.
I just figured out what Robert is talking about above:
In the Resource Browser, (where you would pull up a set of windows or fixtures) click on the pull-down list under "Files and Folders", and go all the way to the top where your file name should be listed. In the window below, you should see all the 'plugged-in' elements in your drawing. Somewhere in all of that should be the "root" ID symbol that you're having trouble with. (In my case the "Door ID 1-48". Single click on that symbol to select it, then right click and go up to 'Edit'. A dialog box will appear with the heading "Edit Symbol". Select "2D Component" and click the "Edit" button. This symbol will appear by itself in your main window. Click on just the text element to select it and look in the Object Info window. You should have options to set the font and size of the text in the symbol. Make your changes and click on the "Exit Symbol" button on the upper right corner of your main window. All the instances of your ID symbol should update to reflect the change you made. Ta Da!
(But the annoying thing is: why were the window symbols OK, but the door symbols messed up in the first place?)