If you selected an automatic play option and want to change it, you need to delete the old action in the file manager (PCManFM) preferences.
- Raspberry button -> Accessories -> File Manager
- Edit -> Preferences
- Volume Management
- In the Don’t show available options for … text box select the media type you want to change and click Remove selected
Now when you next insert that type of media you will get the dialog box that lets you assign an auto play program.
If you no longer want the auto play selection dialog to open, uncheck the Show available options for removeable media when they are inserted check box