On Windows 10;

Goto C:\ProgramData\ComposerSetup\bin

Edit: composer.bat and add memory_limit=-1 in the last line as shown below.

@echo OFF
:: in case DelayedExpansion is on and a path contains ! 
setlocal DISABLEDELAYEDEXPANSION
php -d memory_limit=-1 "%~dp0composer.phar" %*