It seems that the demo does not give access to the Settings menu, so you can't see the workflow editor.

Still, you can go to the runbot and connect on an instance. The runbot instances are for tests purposes and may be broken.

The steps to see the workflow editor are:

• Go to Settings > Technical > Workflows > Workflows.
• Click on the workflow you want to edit
• Change the type of view to Diagram in the right upper corner

If you don't see the menu, you have to give more accesses to your user, edit your user and add the Accesses Rights Technical Features and Administration / Settings. (you'll need to refresh the page to view the new menus).

[EDIT] according to Daniel's comments.