1. Select “Background Layers” group.
  2. Select the layer named «Background»
  3. Double click on smart object thumbnail.
  4. The window with smart object will open. Create new layer (Menu/Layer /New/ Layer) and just Drag & Drop your design upon the layer. Make sure that image fits the size of a smart object. If it doesn’t, please, use any transform tool (usually Menu/Edit/Free Transform) to make design fit the smart object. Keep primary aspect ratio.
  5. Click «Save» from menu (or use cmd+S (on mac) or ctrl+S (on pc)).
  6. Return to window with your mockup. Design of the product will change in few seconds.

Posted in: Mockups