Here’s how you do it. There are two .PNG files in the Zip file. Extract them both into C:\Program Files (x86)\xu4\graphics\png (or your respective path). After that, run xu4. From the title screen choose Configure. Then Choose Video Options. Select Game Graphics Options. Repeatedly choose Graphics Scheme until it cycles to VGA-ALLPNG. Once there, Return to Video Options at the bottom. Then Use These Settings then Main Menu. You should already notice the new tileset and fonts.