Step 1. Extract updater.zip to your PC.

Step 2. Copy Entire updater folder to your USB device.

Step 3. Plug USB device into DSM-510.

Step 4. Go to options/setup, select Software update. Choose Update from USB, and hit next.
New firmware should be detected, hit next again to install.

Step 5. Allow DSM-510 time to update device and when prompted, hit OK to reboot.
