'laravel' is not recognized as an internal or external command, operable program or batch file

I'm trying to install laravel 5.4 on my system, I have followed steps to install it but I'm not sure where I'm doing mistake. I'm using windows 10, When I run command

composer global require "laravel/installer"

It shows error "Content length mismatch".

laravel new myproject

'laravel' is not recognized as an internal or external command,
 operable program or batch file.

php -v output :

 PHP 7.1.1 (cli) (built: Jan 18 2017 18:51:14) ( ZTS MSVC14 (Visual C++ 2015) x86 )
 Copyright (c) 1997-2017 The PHP Group
 Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies

Also I have added "C:\Users\AAMIR\AppData\Roaming\Composer\vendor\bin" to Path variable in environment variables. Now I'm stuck on this issue. Any help is much appreciated. Thanks.

via Aamir