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

Official WIKI page: openmodeldb

License of use it: CC-BY-4.0

HOW TO INSTALL:

Rename the file from: hfa2k_v1.pt to 4xHFA2k.pth

Copy the file 4xHFA2k.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