You’ll find a quick tutorial here.
In most cases you don’t need the converter at all, you’ll find all you could need in the download pages.

These scripts allow you to upscale default Minecraft resourcepacks to your desired resolution.
This is useful for shaders like SEUS PTGI that requires all blocks to be the same resolution for POM and reflections to work.
If you have an incomplete pack and notice issues on missing blocks (falling back to vanilla textures), then use these.