When you launch Assist your Snap should be in the list, then select Advanced. This will drop you into a upgrade utility. You will be prompted for the admin PW, then select the upgrade file. Follow the instruction on the screen. You will be prompted to put the snap into FLUP mode. The instruction are here
http://wiki.procooling.com/index.php/Snap_Server_Resets . Wat for 30-45 sec before continuing after putting the server in FLUP mode.