Instructions
Turn on your PS3 if it's not on already.
Connect the USB device to the PS3 and log into your account.
Navigate horizontally to the "Game" section of the XMB menu.
Navigate vertically to the "Saved Data Utility (PS3)" option and select it.
Select the USB device displayed in the list.
Locate and highlight the save game you want to copy.
Press the green triangle button on your controller or PS3 remote. This brings up all available actions for the save file.
Select "Copy" from the list of options.