Photoshop - layers

[Nancy Holtz]

I am not I have to need to change/replace the image shown in the back wall of the attached elevation illustration elevation as shown. What is the best or how to do it? Can someone help or advise? 

[Leslie Moak Murray]

Here's one way:

Duplicate the layer. Select around the image you want to remove.

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Edit>Cut (on the duplicate layer)

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Drag the replacement image in and put it between the orignal layer and the duplicate. Postition it, and if it's too big, reselect the square, Select>Inverse>Cut.

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Select the rectangles which are blocking the replacement image - my screenshot shows the bottom layer selected, but you're going to cut on the top duplicate layer (sorry!):

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With your replacement image layer selected, Edit>Cut