I recently had to upgrade a Windows IIS Server running PHP 5.5 to PHP 7.1.1. I ran across this excellent blog post which got me 99% of the way through the process. Some things I had to do additionally/differently: Because mine was an upgrade, and not a fresh installation of PHP, I had to remove old "Handler Mappings" that tried to point to the old PHP5.3 directory/executable. I had to do this (remove old PHP mapptings) a second time, on the individual 'site' in the IIS Manager on the server. It wasn't enough to to it at the IIS Server level. One of my sites uses MS SQL Server, so I needed to update the phpsqlsrv_ and phppdosqlsrv dll's, too. I ended up getting them from the Microsoft Drivers for PHP for SQL Server page directly (for PHP 7.1.1, on Windows Server x64, the SQLSRV40.EXE download held the right files for me). It's also worth mentioning that, while the Microsoft Web Platform Installer (Web PI) was available on this server, it kept getting 401 errors when trying to download packages. The best I could determine, it looked like firewall rules were preventing Web PI from reaching the packages it needed. So, I was left with the above-described manual upgrade process.