This upscaler is not mine, all the credit goes to: KIM2091

Official WIKI page: openmodeldb

License of use it: CC-BY-NC-SA-4.0

HOW TO INSTALL:

Rename the file from: ultramix_Smooth.pt to 4x-UltraMix_Smooth.pth

Copy the file 4x-UltraMix_Smooth.pth inside the folder: stable-diffusion/models/ESRGAN

Restart/Reload you Stable Diffusion instance

The upscaler should be visible for hi-res and extras tabs