Instructions
Turn on your PlayStation 3 and wait for the dashboard to load up. Plug your external storage device into the USB slot on the front on your PS3 console.
Press the "Right" arrow and select "Games," then press the "Up" arrow and select "Saved Data Utility."
Scroll down and locate the saved game you would like to compress. Press the "Triangle" on your controller and select "Copy." Select the external storage device as the place you would like to copy the file to.
Remove the external device from your PS3 once the copy has been made and place it into the USB slot on your computer. You will find this slot on the side of a laptop and on the rear of a computer tower unit.
Click on the "Start" button and select "Computer." Select your external storage device from the list of devices.
Right-click on the saved game file within the device and select "Send to" from the drop-down menu. Select "Compressed (zipped) folder." This will make a ZIP file copy of the saved game next to the original within the external device. Delete the original and you will be left with the compressed game backup file that you can eitter keep on the USB drive or send to a hard drive for safe keeping.