Website administrators and translation managers can easily enable Advanced Translation Editor.

This can be done using the Translation Management Wizard or on the WPML -> Settings page.

Activation using the Translation Management wizard Activation on the WPML -> Settings page
Activation using the Translation Management wizard Activation on the WPML -> Settings page

After selecting the Advanced Translation Editor option, it will become the default translation editor for all translators in your site.

The translation manager will get an email notification and can change the usage of Advanced Translation Editor for individual local translators. They can do this by clicking on the Manage translator access link in that email.

The dashboard for configuring the Advanced Translation Editors for your translators
The dashboard for configuring the Advanced Translation Editors for your translators

If, by any chance, a translator is not listed on this page, go to the WPML -> Settings page and in the How to translate posts and pages section click Synchronize translators and translation managers. When the synchronization is over you should be able to select translator that was not listed.