Step 1: Let's say we got this 1360x768 wallpaper but we want this to be good for 1024x768. If you apply this without re-size it correctly you will get a squeeze effect, not something you really want. So, open Photoshop and create a new canvas with the desired resolution, in our case 1024x768. Now open the wallpaper you want to resize. Go back to 1024x768 canvas and duble click on layer to unlock it.
Step 2: Now holding CTRL left click on the little white square to select the layer.
Step 3: Now hit CTRL+C to copy the selection and go to the wallpaper file to paste it on top of it. You should have something like this.
Step 4: Now fit the new copied layer on top of the wallpaper until you have something you like. Remember, only whats under the white layer will be copied to the new wallpaper. What we have now i think should work pretty well. Select the wallpaper layer and again holding CTRL left click on the little white square from the copied layer to make a selection on the wallpaper.
Step 5: Hit CTRL+C to copy, now hit CTRL+N to create a new canvas, press ok, and now hit CTRL+V to paste your selection on the new created file. Go on top menu, File, Save As, enter desired name and format and save your new wallpaper.
Done!
Quick tutorial: Revers mode, 1024x768 to 1360x768. Create a new canvas 1360x768 or whatever you want. Make the background black with the Paint Bucket Tool, and copy the wallpaper on top of it. Save your file. Done. The only downside of this process is that you will end up with a wallpaper that haves black lines on sides.
