Hi there,
First you need to check that the user you are using is a super admin. It doesn't show up with other inferior user roles.
Second: The plugin only works if WP Super Cache is active. Please check that it's active.
If both plugins are active, you will find an additional menu entry in the header of the WordPress administration.
Here you can see a screenshot of the spanish version in english it will be at the same place and read: "Clear all cached files".
I hope this will help.