Hi)

To replace old "pano_A" with a new "pano_B" inside a tour you need to do the following:

1) Create a new folder and paste your pano jpg inside it. Drop jpg onto Make Vtour Multires droplet and wait until it finished. If view settings of this new pano are different than those from the old pano, then open Tour Editor and adjust view settings. Save xml to this folder.
2) In your tour, go to folder "panos" and delete folder "pano_A.tiles"
3) inside scene named "scene_pano_A" delete "image" section of the code
4) From the newly created "tour.xml" copy "image" section of the scene and paste it inside "scene_pano_A" node and "view" section (if view settings are different). Also, copy folder "pano_B.tiles" to "panos" folder of your tour.
5) Inside the scene "scene_pano_A" replace all occurences of "scene_pano_A" with "scene_pano_B" (in scene name, in thumburl reference, in preview setting and inside webvr image path).
6) Now your pano is ready, but it has new name, and there are some hotspots which referred to it. So you need to either replace all occurences of "scene_pano_A" with "scene_pano_B" inside "linkedscene" attributes of the hotspots, or keep the old scene name.

Maybe, there's some easier way to replace pano, but I always do it this way.

Yep, right, no need to replace html file. However, if you want to update Krpano version also, then you'll need to replace tour.js, tour.swf and all plugins you used in the tour with newer ones.

EDIT: I usually resupply the whole tour folder - just to be sure client doesn't place the filles in wrong place and doesn't screw everything up.