Go to Settings > Users & Rights > User Management and then search for the user you wish to change the profile for.
Either click on the name of the user or the editing "pen" symbol all the way to the right.
The last step is to click on "Set user profile". A drop-down menu with all available profiles will appear and you can choose the desired one there.
This description is written based on a standard Bynder setup The environment you use might have different settings, additional modules or custom changes. Thus, your particular situation may vary.