How to Get Thumbnails to Display Larger Images
In Windows and Mac OS X operating systems, thumbnails or icons display your folders, pictures and programs. They allow you to identify what the component is before opening it. If you are unhappy with the current size of your thumbnails, you can increase their size and enhance their appearance. This is a personalization preference and does not affect the program or picture using the thumbnail.
Windows 7 Users
Launch the folder in which you want to change the thumbnail and file details.
Click the drop-down arrow next to the "Views" button on the toolbar on the top of the folder's window.
Scroll down the pop-up menu and select the thumbnail size you want to use. Select "Large" or "Extra Large" icons to increase the size of your icons and thumbnails.
Mac OS X Users
Right-click any part of the desktop and click "Show View Options." A new dialog box launches.
Drag the slider under "Icon size" to the right to increase the thumbnail sizes.
Close the dialog box. The thumbnails should be larger.