Software needed is Paint.NET.
1. Open two images you wish to use as the icon and cover art for a game in Xexmenu.
2. Resize one image to 512x512 pixels to use as icon and 2048x2048 for the 2nd picture to use as cover art.
3. Simply save the icon image as (icon.dds) and save the cover art image as (nxebg.dds)
4. Copy the two files to your extracted iso game folder and you're Done! the artworks you created should appear in xexmenu.
Alternately you may wish to edit existing icon.dds and/or nxebg.dds files.