A well accepted practice in the software development world is to run major software updates through a series of tests before running them on the live site. This allows the developer to catch as many bugs as possible before putting the changes in front of users. Unfortunately, that’s not a practice that many WordPress site owners employ.
Most WordPress updates come with the standard warning that you insure you have a fresh backup of the site before running them. But the support forums are full of panicking site owners asking for help: “I just updated <WordPress, a theme, or a plugin> and now <some function> is not working! How do I get it back?” so it’s pretty obvious that even that level of caution is often ignored.
Many site hosts (SiteGround, some GoDaddy plans, etc) offer the ability to create a staging site – essentially a mirror copy of the live site with a different web address – with just a click or two, at no extra cost. Ask your host if that’s available for yours. If your host doesn’t offer staging sites we can set you up with one for a fee – contact us for details.
Ideally, you’ll upgrade your staging site and give it a run through to make sure everything looks right and functions correctly. Check things like menu drop-downs, contact forms, product ordering pages (have a cheap test product as a draft – or use a real product and cancel the purchase afterwards), embedded videos, site banners, as well as the general layout. If anything is broken, get it fixed and re-tested before moving forward. If possible, make those same fixes on the live site before upgrading it.
Once everything checks out OK on the testing/staging site, take a full backup of the live site, then perform the upgrade there and re-test. Sometimes there are bugs which only show up on the live site, despite your having passed all the tests on the staging site!