All the installation guides and upgrade guides for Sitecore products are distributed as PDFs that you can download from the Sitecore downloads site.
You can download the guides along with the appropriate versions of the software, the relevant tools, and see the release notes for each release.
Here is a list of links to the pages for the most recent releases.
You can download all the installation and upgrade guides for all the other products and versions from the Sitecore downloads site.
You must log in to the Sitecore downloads site before you can download the software or the documentation. If you try to download a resource without logging in, you will be asked to log in and after you have logged in you must click the resource that you want to download again.