To delete a panoramic image:
Log in to your Roundme account;
Open the tour you'd like to update;
Switch to the edit mode;
Click the panorama you would like to delete and hold the button.
Drag and drop the panoramic image to the 'Remove' area in the upper part of the screen:
Please note that your panorama is deleted with all the additional content you add (Hotspots, Portals, locations on the map) ant there's no option to recover it.