Changing Duration from Hour to Day in P6

How do I change the duration from hour to day in P6? In P3 you would just copy the project and select day in the drop down menu.

Our contractor has drawn up a new plan in hours for a 2 year project and I want to convert the durations to days.
I changed the duration format (@edit_user preferences) to day but that only changes the display and when you enter durations it is still in hours.

Please assist if possible.