AI, which isn't always accurate, offers these methods. Worth a try...
"To replace a single image in an already completed NCH Photostage project, follow these steps:
Open your existing Photostage project.
In the Media List area, locate the image you want to replace.
Right-click on the image and select "Edit in external editor"
. This will open the image in your default image editing software (e.g., PhotoPad).
In the external editor, make the necessary changes to the image or replace it entirely with a new image. Save the changes
Return to Photostage. You should see a message saying "Editing in an external editor... Press Ok when done". Click "Ok".
Photostage will automatically reload the updated image, reflecting the changes in your project
Alternatively, if you want to use a completely different image:
Add the new image to the Media List by clicking the "Add Photos" button.
Drag the new image from the Media List to the slideshow timeline, positioning it where you want it to appear.
Delete the old image from the slideshow timeline by selecting it and pressing the Delete key on your keyboard.
Adjust the positioning and duration of the new image as needed.
Remember to save your project after making these changes.