Using the move tool, position the new layer over the window that you want to replace. Due to perspective there is a slight difference in size, but by dragging the boxes in the corners of the selection, I can re-scale the new layer to fit precisely over the background.
With the layer positioned, set the layer opacity back to 100 percent, and then merge the layer back into the background, using the Flatten Image option on the Layer menu.
In order to disguise the fact that the centre window is now a copy of the one on the right, change some of the distinctive reflections in the panes. Using the same Copy/Paste technique, copy a reflection-free pane over one of the ones in the lower half of the window, making it look different from the one on the right.
With a little tidying up with the Clone brush to hide any remaining blemishes or duplicated details, thatâ€™s pretty much it. You can use this technique for many things, from hiding embarrassing zits, losing that tree that looks like itâ€™s growing out of the top of someoneâ€™s head, or eliminating political opponents who have fallen out of favour with your military junta. The possibilities are endless!