Running Composer returns: "Could not open input file: composer.phar"

I am new to symfony2 and reading [symblog][1]. In third chapter while trying with data-fixtures I tried the command: `php composer.phar update` but I got the error: `Could not open input file: composer.phar` So I googled a little and tried php composer.phar install but still getting the same error. So please guide how to deal with this composer to install new extentions or bundles like data-fixtures in symfony2 using wamp. [1]: http://tutorial.symblog.co.uk/#tutorial-parts