After editing the text on the PSD files on a product box or ebook cover (see How Do I Customize the Text on a Print Product? ) follow these instructions to reassemble the box or book shape of the product.
Once the text has been revised, you need to update the final product box.
Have open both your front cover .psd and the final product .psd. For the cover.psd, go to Layer in the top menu and choose Flatten Image.
Drag the flattened layer into the document with the box:
To make it easier to line up, you can temporarily decrease the opacity of your cover image: press the 5 key on your keyboard to reduce the opacity of the layer to 50%.
Press Ctrl+T (Mac: Command+T) to bring up the Free Transform outlines. Click and drag the corners of the cover to the corresponding corners of the front of the box. (To preserve proper dimensions, you can click on a corner and hold down the Shift key as you are resizing it). Press Enter to apply the transformation.
Repeat the same steps for the image of the side and top box. Distort/resize to fit on the left side and the top of the box. Then increase the opacity of the front, side and top layers back to 100% by tapping 0 after selecting each layer.