Step 1 - Save and close everything you've got open but leave the Surface powered on and connected to the dock. 

Step 2 - Click here to download the Surface Dock Firmware Updater and run it.

Step 3 - Click Next

Step 4 - Check the box for I accept, then click next

Step 5 - Leave this as-is and click next

Step 6 - Click the install button and click Yes when it asks for permission

Step 7 - Let it do what it needs to do, then click the finish button

Step 8 - It will ask to reboot. Click Yes and log back into your account after the Surface reboots

Step 9 - Unplug the Surface Dock from the Surface for 5 seconds, then reconnect the dock. Leave it connected for 5 minutes, then disconnect it for 5 minutes. After that, the dock will be updated, can be reconnected, and get back to being used as normal.