INSTALLATION:

1. Download the ZIP file 
2. Within Blender, navigate to Edit > Preferences > Addons > Install
3. Select the ZIP file
4. Enable the addon by clicking on the box 
5. Select Path for the Upscaled Textures in addon's preferences

About Real ESRGAN:

Real-ESRGAN aims at developing Practical Algorithms for General Image/Video Restoration.
We extend the powerful ESRGAN to a practical restoration application (namely, Real-ESRGAN), which is trained with pure synthetic data.

ncnn is a high-performance neural network inference computing framework optimized for mobile platforms. ncnn is deeply considerate about deployment and uses on mobile phones from the beginning of design. ncnn does not have third party dependencies.

This addon is the ncnn implementation of Real-ESRGAN in blender . 

Additional links:

If you want to add another model in the addon you can get the models for this page 

To add custom models to the addon there is an option in addon preferences.