To update php in Plesk versions, first you need to have an root user credentials and then admin access to the Plesk portal.If you are having both then follow the below steps
Step 1: Login in as Plesk Administrator and then go to Tools & Settings on the left pane
Step 2: Then under Plesk section you will see updates & upgrades, Click on Updates & Upgrades
Step 3: Once you click on “Updates & Upgrades”, it will redirect to a link like
https://sitename:8447/?secret=xxxxxxxx&locale=en-US
If the link with your sitename is not opening, then replace it with your ip address & then it will open up as shown (If you see a login box, then you may need to login with username/password on it)
Step 4: Then click on Add/Remove components, In the next screen you will see a lot of components, scroll down & then you will see a webhosting component
Step 5: In the Webhosting component, you will see a lot of components as shown below, To install a php component, click on the “+” icon next to it
Step 6: You will see a list of Php components as shown below, you can choose to install/uninstall any component as shown below
Once you select a component, click on “Continue”, it will install the component.