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: 4xlsdirplusn_v1.pt
to 4xLSDIRplusN.pth
Copy the file 4xLSDIRplusN.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