How do I make a different position the main one?

Usually, the current position will be shown as the main one at the top of the list, but if a person profile has more than one current position, you can choose which one you want to be at the top of the list.

Click the pencil icon on the position that you would like to make the primary, and scroll down to this section.  

Turn the switch on and save the record - the role will be made primary and moved to the top of the list.