The recommended way in the documentation is via admin:
System > Web Setup Wizard > System Upgrade.
(http://devdocs.magento.com/guides/v2.0/comp-mgr/upgrader/upgrade-start.html)
You must have crons enabled or it will not work.
The second way is with composer:
In composer.json change this line
"magento/product-community-edition": "2.0.0",
Also you should change the line 5 as well "version": "2.0.0", to keep it in sync.
to whatever version you want, and then run:
composer update
php bin/magento setup:upgrade
php bin/magento setup:static-content:deploy