You can select this pop-up menu option when you right click with the mouse button on any topic displayed inside the topic tree tab. But the balloon help that is displayed when you hover with the mouse is misleading you.
For example lets say you have Continent (topic type) and Europe (topic instance) open inside the topic tree tab. Open Europe topic on the traditional topic panel. Right click with the mouse on Continent, select "Associations", and hover your mouse over the "Make superclass of current" option.
The pop-up help text for this menu option says "Make context topic ***subclass*** of the current topic open in topic panel. This is wrong, it should say ***superclass*** instead.
Not a big deal, but useful to know for fixing it in the next version.