There is nothing you have to do but click the menu item.
WampServer will then restart Apache automatically, and within a few second you will be using the new PHP Version.
As to preparation, I would first chcek that whatever PHP code I was running was compatible with the version of PHP I was considering moving to.
I may even install a new WAMPServer on another machine to test this !!!
As Oto says, if the code does not run on the new version, another 5 seconds should allow you to click the Original PHP Version on the menu and get back to where you started from.
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(Windows 10 Pro 64bit) (Wampserver 3.3.4 64bit) Aestan Tray Menu 3.2.5.4
<Apache versions MULTIPE> <PHP versions MULTIPLE> <MySQL Versions MULTIPLE>
<MariaDB versions MULTIPLE> <phpMyAdmin versions MULTIPLE> <MySQL Workbench 8.0.23>Read The Manuals Apache --
MySQL --
PHP --
phpMyAdminGet your Apache/MySQL/mariaDB/PHP ADDONs here from the
WAMPServer alternate Repo-X-X-X-
Backup your databases regularly Here is How dont regret it later! Yes even when developing -X-X-X-