Before starting, switch the Render Engine from EEVEE to Cycles, as this may prevent Blender from intermittently hanging during the process.
Avoid opening the Material Properties or clicking the Slot Menu or Material Selector buttons in the Shader Editor during this process, as it can rapidly consume significantly more memory and cause Blender to crash if it's exceeded.
Ensure you've downloaded the most recent versions of the assets.
To use the Head Textures with the Arm Textures, put both sets of textures in the same folder first.
Open the Skin material in the Shader Editor and unmute (M) the muted Image Texture nodes.
Load Skin Albedo.1001.png into the Image Texture node that's connected to the Skin node's Albedo Image input socket.
Load Skin Subsurface.1001.png, Skin Roughness.1001.png and Skin Displacement.1001.png into their respective Image Texture nodes, and set their Color Space to Non-Color (see image on right).
Load Skin Wrinkles A.1001.png and Skin Wrinkles B.1001.png into their respective Image Texture nodes (if they're muted, press M to unmute them).
Set their Color Space to Non-Color.
Be sure to set the appropriate Cycles Render Device in Edit > Preferences > System, and select GPU Compute (if available) in Render Properties to maximise rendering speed.
The following example settings can be applied using the Skin Shader, however similar tones can also be achieved in image editing software by layering the Albedo over the Base colour image and adjusting the HSV of both layers. Tip: for lighter tones, try reducing the Saturation instead of increasing Value (which tends to also increase the saturation).
Individual layers for the Albedo, Displacement and Wrinkle maps are included, so they can be treated independently in image editing software. This makes it easier to modify the wrinkles without affecting the pores, for example.
The Albedo layers (where available) should be stacked in the following order. Duplicate a layer to increase its opacity.
Blemishes
Wrinkles
Veins
Mottling
Shading
Base
The Displacement layers should be stacked in the following order, with the blend modes and opacities indicated (for mid-range values):
Wrinkles (opacity 20%, blend mode: Overlay)
Blemishes (opacity 20%, blend mode: Overlay)
Pores (opacity 20%, blend mode: Overlay)
Neck Veins (opacity 25%, blend mode: Normal)
Face Sculpt/Neck Base (opacity 100%, blend mode: Normal)
The Wrinkles layers should be stacked in the following order, with the blend modes and opacities indicated:
Pores (opacity 10%, blend mode: Overlay)
Sculpt (opacity 100%, blend mode: Normal)
For Scalp & Neck Wrinkles A, use Skin Displacement.1002 as the Base layer
You may find it necessary to resize some of the images to preserve memory, especially with 8GB of RAM or less. To retain the highest quality, prioritise the resolution of the displacement, followed by Albedo and Roughness, with Subsurface being at the lowest resolution.
To achieve the highest quality results, make sure Displacement & Bump is selected in Material Properties > Settings > Surface > Displacement, and set the object's subdivision level as high as your hardware permits. This allows the finer bumps to displace the geometry and cast shadows, as well as interacting with the SSS more realistically. Deleting geometry that is outside the view can provide more headroom for further subdivisions.
Attention: Keep a close eye on your memory usage while testing subdivision levels, as overdoing it can quickly exceed the available RAM and cause a hang or crash. Also, if EEVEE is enabled instead of Cycles, merely selecting a shader node or material may cause the memory usage to massively surge.
In a similar vein to the above, the higher the sample level, the less noise - but also the greater the apparent realism. And while denoising produces smoother results, it tends to smear away the fine details and also contributes to less convincing renders at lower sample levels.