On the Components overview page, you can see all the components (plugins, themes, and WordPress core) that each of your sites has.
The table shows, which of the components are vulnerable and which are just outdated.

Updating the Components

You can update your components on that page. Keep in mind to backup your files and databases before doing that.
If you wish to update components individually, you can select those one by one by clicking on the checkbox on the left column. After that, click on Action and Update.
Your components' versions should start updating on your WordPress sites.

Another way is to bulk update all components across all your sites. For that, click the green Update All button. You will be asked for confirmation.