After you have unzipped your print product and installed any new fonts (see Unzipping the Template and
How to Install a New Font ) you may change the ../images in Adobe Photoshop or Adobe Illustrator.
Launch Photoshop and open a .psd file from the product's "psd" folder. Select the layer with the image you wish to change. Right-clicking on an image on the screen will highlight its layer in the Layers panel. Then, Ctrl-click on the Layer's thumbnail in the Layers panel and the image on that layer will be selected:
Open the new image that you've prepared (File > Open). From the top menu, choose Select > All, then choose Edit > Copy. Then, click on the print product .psd's top bar to make it the active window, and choose Edit > Paste Into. This places your new image into a mask selection so it will be the same dimensions as the original image. You may use the Move Tool to move your pasted image around within the mask borders until you have it the way you want it. You can also use Edit > Free Transform from the top menu if your new image is a little too big or too small.
The picture above shows the new image on the left and, on the right, after it is pasted into the print product's .psd. The black and white thumbnail picture in Layer 16 denotes that the image has been pasted into a mask. The pasted image will not display outside of the borders of this mask.
Open the new image that you've prepared (File > Open). Illustrator allows Layer masks/Clipping masks on vector art only, so if your new image is not vector, it's suggested that you have it already cropped and resized to fit into the print product's .ai file. Click on the new image and drag it into the print product .ai file. If necessary, click on the pasted image and, holding down the Shift key to retain proportions, resize the image to fit into the design.
The picture above shows the new image selected, on the left. And on the right, the image pasted into the print product's .ai file.