How to install Unity packages?
After you downloaded your copy, simply drag and drop the package file into the Project folder as usual.
How to update materials to URP or HDRP?
Create a backup copy of your project. Navigate to Assets > Deadly Dungeons > Infernal > URP HDRP. Click on the one package you wish to use. Important: by unpacking this file, it will overwrite the Materials in the original package.