You can change php version of composer without uninstalling it, follow these steps :

1. Search for system environment variables in cortana.
2. Click on the button "Environment variables".
3. Under "System variables" select path and click on edit, you will see one entry like this "C:\wamp\bin\php\php5.6.13".
4. Just change this to the folder name of the php located at your wamp/bin/php7.1.9, here php7.1.9 is folder name.
5. Replace php5.6.13 with bin7.1.9, it will look like these "C:\wamp\bin\php\php7.1.9", just click ok on all the boxes.
6. You are done.
7. To verify, first close all the cmd windows, than open cmd and type php -v, press enter and you should see php7.1.9.
8. If you don't see change in php version than just restart your pc and run php -v again in cmd , it will work.

I'm assuming Windows if you're using WAMP. Composer likely is just using the PHP set in your path: How to access PHP with the Command Line on Windows?

You should be able to change the path to PHP using the same instructions.

Otherwise, composer is just a PHAR file, you can download the PHAR and execute it using any PHP:

C:\full\path\to\php.exe C:\full\path\to\composer.phar install

If anyone is still having trouble, remember you can run composer with any php version that you have installed e.g. $ php7.3 -f /usr/local/bin/composer update

Use which composer command to help locate the composer executable.

Another possibility to make composer think you're using the correct version of PHP is to add to the config section of a composer.json file a platform option, like this:

"config": {
    "platform": {
        "php": "<ver>"
    }
},

Where <ver> is the PHP version of your choice.

Snippet from the docs:

Lets you fake platform packages (PHP and extensions) so that you can emulate a production env or define your target platform in the config. Example: {"php": "7.0.3", "ext-something": "4.0.3"}.

I found out that composer runs with the php-version /usr/bin/env finds first in $PATH, which is 7.1.33 in my case on MacOs. So shifting mamp's php to the beginning helped me here.

PHPVER=$(/usr/libexec/PlistBuddy -c "print phpVersion" ~/Library/Preferences/de.appsolute.mamppro.plist)

export PATH=/Applications/MAMP/bin/php/php${PHPVER}/bin:$PATH

Old question I know, but just to add some additional information:

• WAMP is used only on Microsoft Windows Operating Systems.
• Changing the version of PHP used through the left-click -> PHP -> Version menu changes the version used by Apache to server your site.
• Changing the version of PHP used through the right-click -> Tools -> Change PHP CLI Version menu changes the version used by WAMP's PHP CLI.

Note: It is important to understand that the "PHP CLI Version" is used by WAMP's own internal PHP scripts. This "PHP CLI Version" has nothing to do with the version you wish to use for your scripts, Composer or anything else.

For your scripts to work with the version you require, you need to add it's path to the Users Environmental Path. You could add it to the Systems environmental Path but the Users Path is the recommended option.

From WAMP v3.1.2, it would display an error when it detect reference to a PHP path in the System or User Environmental Path. This was to stop confusion such as you were experiencing. Since v3.1.7 the display of this error can now be optionally displayed through a selection in the WampSettings menu.

As indicated in previous answers, adding an installed PHP path (such as "C:\wamp64\bin\php\php7.2.30") to the Users Environmental Path is the correct approach. PS: As the value of the Users Environmental Path is a string, all paths added must be separated with a semi-colon (;)

After experiencing the exact same problem (IE: Choosing which version of PHP I wanted Composer to use), I created a script which could easily and rapidly switch between PHP CLI Versions depending on what project I was working on.

The Windows batch script "WampServer-PHP-CLI-Version-Changer" can be found at https://github.com/custom-dev-tools/WampServer-PHP-CLI-Version-Changer

I hope this helps others.

Good luck.