Where exactly do you right click ? The content of the contextual menu is of course contextual. So you have to right-click on a single scene in the main workspace to be able to have this entry in the menu. If the right click does not select the scene, select it before right-clicking.
This feature is available in the Pro version of course, but not in the standard version.
Below below the caption "Since Panotour 2.5 [...]" it says "Replace Panorama File: Instead of deleting and adding again, this function allows to replace a scene without disturbing the project."
It seems clear that this is a not a Pro feature.
For clarity, I would suggest putting an asterisk beside features that are Pro only.