It depends on the CMS. Some CMSs have the option to publish HTML files. We couldn't begin to explain how to do this with each of hundreds of CMSs.
If your CMS has a server-side cache, there may be little if any point in doing this, though. Generally, though, a CMS won't cache pages for logged-in users, since pages could vary from user to user. (A really smart CMS would cache pages for logged-in users as well - you'd have to be careful to avoid unique per-user/per-visit content.)
If your CMS doesn't have this option, you will need to use a tool that can capture the HTML from your site, which you can then upload to a static site (or static section of your site). HTTrack is a good starting place.