As announced on the main PHP.net site, the latest release candidate for the PHP 7.2.0 series has been made available for download: Php 7.2.0 RC3.

The PHP development team announces the immediate availability of PHP 7.2.0 RC3. This release is the third Release Candidate for 7.2.0. All users of PHP are encouraged to test this version carefully, and report any bugs and incompatibilities in the bug tracking system.

[...] For source downloads of PHP 7.2.0 Release Candidate 3 please visit the download page, Windows sources and binaries can be found at windows.php.net/qa/.

You can find out the changes that happened in the latest NEWS file and find out how to upgrade your installation in the UPGRADING guide.