A supersaver upgrade is an upgrade from 2nd class to 1st class. It assumes you already have a 2nd class ticket, or a pass. It is intended mostly for people who have a 2nd class travel pass that occasionally want to travel 1st.
The upgrade ticket allone is not sufficient for travel.
Note that with only 5 days you will have to temper your ambitions. For visiting the cities you mention, and travelling the Bernina and Glacier Expresses you would need 10 days or more.
My suggestion is to just go to one location (eg Luzern) and spend your time exploring and enjoying the area. That will also save you quite some money too.