Instructions
Select an appropriate USB device. The Xbox 360 supports USB devices between 1 and 16 GB.
Remove any important data from the USB device prior to beginning the process, as all information will be removed permanently. Once the device is ready, insert it into an Xbox 360 USB port.
Turn on the Xbox 360, then navigate to "My Xbox," "System Settings," then "Memory."
Select "USB Storage Device" from the "Storage Devices" screen.
Select "Configure Now" and confirm the process if you would like to use all of the storage space on the USB device for the Xbox 360. If you would like to use only a portion of the device for the Xbox 360 (or have more than 16 GB available on the device), select "Customize." Move the slider to select the total space on the USB device you wish to dedicate to use with the Xbox 360, then press the "A" button to complete the process.