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. Make sure in configuration you have your keys inserted. If it freezes with no output in the logs you can check the php logs to see if it timed out and then increase the memory_limit in .htaccess to 2G.
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