This upscaler is not mine, all the credit goes to: XINNTAO
Official WIKI page: openmodeldb
License of use it: BSD-3-Clause
HOW TO INSTALL:
Rename the file from: realesrganX4Plus_v1.pt
to RealESRGAN_x4plus.pth
Copy the file RealESRGAN_x4plus.pth
inside the folder: stable-diffusion/models/RealESRGAN
Restart/Reload you Stable Diffusion instance
The upscaler should be visible for hi-res and extras tabs