That's not a cassette; it's a SunTour "New Winner" freewheel. To remove it from the hub, you need the proper two-prong remover tool to fit the wide notches in the freewheel body. The other, narrower notches are to adjust the bearings, for which you need a special tool. Chances are, that will be unnecessary; if it is necessary, let a bike shop or Pastor Bob deal with it.