As of 5.6, site administrators will be able to proxy log in as another non-administrator user. This means they can view the site as that person, and they will be able to navigate as if they are logged in as that user.
Please note that another article has been written detailing what you can do when impersonating another user, found here
Within your site, navigate to Site admin:
The Site admin screen will be displayed. Within the Site admin screen, navigate to User management > Users:
The Users screen is displayed, listing all users within that site, and also labelling whether they are a System administrator or not. Find the user you wish to impersonate and click More actions > Impersonate User:
The following message will be displayed:
Informing you of the limitations and settings that will be applied when you are impersonating that user. Click OK. You will now be impersonating your chosen user within the site. The following message will also be displayed:
