How to get rid of the frame (box) around pie charts and other part of whole graphs

There is a bug in Prism 6 (up to 6.04 win and 6.0d mac). Sometimes parts-of-whole graphs are created with a box or frame, and it is impossible to get rid of it.

If you are in this situation, follow these steps:

1. Delete the graph(s) with the unwanted frame. It is not possible to remove the frame from this graph. 
2. Go to Preferences, and to the New Graphs tabs.
3. Change the setting to No Frame (screen shot below).
4. Go to the data table. 
5. Click New...Graph of existing data. Choose the kind of parts of whole graph you want.