How to upgrade PHP on Windows XAMPP
Unlike on unix, there isn't a specific command to "just upgrade" an executable. This makes everything so much more difficult. But there is a way to upgrade your PHP version without copying your giant data folder (the one within the mysql directory of xampp).
Download XAMPP
It begins with the download of the latest XAMPP version. After that, install it in a directory (doesn't matter where). You only have to install Apache and PHP.
In my case, i have XAMPP installed in C:\xampp. My new version is installed in C:\xampp2. It's important that you remember your directories.
Please also shut down Apache and MySQL in your XAMPP control-panel
Install PHP
I really recommend, that you make a backup of your PHP.ini file. This file is located in C:\xampp\php\php.ini. After making your backup, open the C:\xampp2\php\php.ini file, search and replace all occurences of xampp2 with xampp.
After you've done that, you can delete the whole C:\xampp\php folder and replace it with the C:\xampp2\php folder.
Install Apache
You have to do something similar to the PHP installation with Apache. Search and replace xampp2 with xampp in the following files:
C:\xampp\apache\conf\httpd.confC:\xampp\apache\conf\extra\httpd-xampp.confC:\xampp\apache\conf\extra\httpd-ssl.conf
All files can be accessed via the control-panel of XAMPP. All you have to do is click on Apache's Config button and you will see all of them listed.
Then you can delete the whole C:\xampp\apache folder and replace it with the C:\xampp2\apache folder.
Now, everything should check out if you start Apache and MySQL from your XAMPP control-panel.
If not, open your Terminal (WINDOWS + R, Type cmd) and cd C:\xampp\apache\bin. Then execute httpd.exe by typing it into the terminal.
The error, why Apache won't start is displayed now below and you can google for it.
Install XDebug for PHP
XDebug is one of the most installed PHP-Debuggers. To install it, you can have a look at my Tutorial on how to install XDebug.