The Thumbnails Tool is located on the View tab and offers several ways to view Thumbnails:

To use the Thumbnails Tool for viewing:
    - Click on the Thumbnails Tool. The Thumbnails pane displays:
        
    
 
    - Click on the scrollbar to scroll down and view additional thumbnails:
 
    
    - Click on and drag the slider to the left to reduce the size of the thumbnails:
        
   
     
    - To further reduce the size of the thumbnails, click on the slider and drag it all the way to the left:        
 
    
    To enlarge the size of the thumbnails, click on the slider and drag it all the way to the right. 
    - You can also click on the dotted area to resize the Thumbnail pane. Click on the dotted area and drag it to the right or left as desired:
 
    
     Drag the dotted bar to the right to expand the pane:
    