Updating your PHP version should not be a problem, but we can’t guarantee that it’s not. WordPress itself works with PHP versions as far back as 5.6.20 (we’re currently recommending version 7.3, so this is great backward compatibility!), but we don’t know if your themes or plugins will work. They should, and popular or reputable ones almost certainly will be, but we can’t guarantee it.
There are a couple of steps you should take to mitigate any risk before proceeding:
- Make a backup of your website: a backup will let you revert your site to how it is right now in the event anything goes wrong. There are plenty of free backup plugins available, so if you don’t have a backup solution already – use one