To change the default bullet style in PowerPoint, the following steps should be taken:

1. Open the PowerPoint presentation you want to improve.
2. Select the text box that holds the bullets you want to change.
   
3. Navigate to the ‘Home’ tab on the ribbon.
4. In the ‘Paragraph’ section locate the ‘Bullets’ drop-down menu.
   
5. Choose the type of bullets you want to display and hit ‘Enter’ to apply it.