how to update composer

Hello!
I have installed fresh copy contao 4.5.x, but can't login to admin
I check composer -V -> result 1.1.1
Hot to upgrade it in latest 1.6.4?
thank's for help!
Goran

Code:

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$ composer self-update

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or

Code:

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$ wget https://getcomposer.org/download/1.6.4/composer.phar

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