These commands will install composer binary in composer.phar file in current working directory. You may try to verify this by running php composer.phar -v command. composer command will most like point to some global installation in your system – you need to move new binary to correct place, so it could be recognized as global command (see docs):
mv composer.phar /usr/local/bin/composer
If you have already Composer installed, you should able to use self-update command to downgrade to any version:
composer self-update 1.4.1
or
sudo -H composer self-update 1.4.1