After spending a little while in Steam beta Fallout 4's High Resolution Texture Pack is now fully available. All you need to do is to head on over to Steam and press that shiny green download button, but do be warned as its a ridiculously large update, totaling at nearly 60GB in size!
Besides the need for 60GB of extra disk space, the High Resolution Texture Pack also requires an Intel Core i7-5820K CPU, 8 GB of RAM, and a graphics card as powerful as the GTX 1080 8GB. As you can see, those are some pretty damn steep system requirements, and that's just the minimum! As for whether the High Resolution Texture Pack is even worth all of the trouble, that's a bit more difficult to figure out.
I haven't tried it myself, so take the following with a grain of salt, but the Steam reviews are currently painting it as a bit of a mixed bag. On one hand its a free update that makes Fallout 4 just a little bit prettier, but on the other hand its an extremely demanding expansion with very few obvious improvements. From what I've seen online the difference is only noticeable when you're looking for it, and even then its usually just a couple of minor textures getting a facelift. Whether all of this is worth the massive download size and system requirements, that is a question you're going to have to answer yourself.