How to know which version of yii2 is being used and how to upgrade to the latest version of yii2?

Run ./yii command, you will get following output:

./yii

This is Yii version 2.0.8.

The following commands are available:

Source: https://stackoverflow.com/a/29271811/1897969

In console in site folder run composer update. And composer will update you Yii2.

If you want to know which version of Yii2 you are using run Yii::getVersion().