This mod increases the texture resolution of the protagonists by 2-3 times their original resolution. This mod aims to improve the quality of the textures of all the main characters of GTA 4 and allows you to see Niko, Johnny and Luis in a new resolution that is more interesting for details. Clothing, hands, attachments, face, and hair textures have all been improved, all of which have been upscaled by the AI and then tweaked manually for "additional" detail.
The installation instructions are in the file itself, however it is so intuitive that I think you can figure it out without it (I'll give a hint: replacing files)