Technically you cannot update PHP from WordPress itself as this needs to be done on the server. If you are hosting the site with a hosting company, simply asking them to update the PHP version for you is all you will need to do.
If you have access to your control panel, such as Cpanel, you can update your WordPress’s PHP version from here. For Cpanel you would simply log into your cpanel and go to “select PHP version”. From here you can select the version you want to use.
Why Update PHP?
Updating PHP has many benefits. Newer versions of PHP tend to be quicker and may help speed up your site and provide more security than older versions of PHP.
Updating PHP also may be required to use certain plugins or themes if they are not compatible with older versions of PHP. WordPress will let you know when its time to update WordPress so that you don’t run into compatibility issues.
Important Notes
Anytime you make any large changes to your WordPress site it is helpful to make a backup just in case if anything goes wrong.
It also may be beneficial to test a newer version of PHP on a development site so that if there are any issues, your live site will remain unaffected.