How to switch position in a vehicle?

[Renzen]

^^^^
Can't figure it out...

[Fino]

Press middle mouse button/whatever button you have for action menu.
Select the seat you desire.

[Renzen]

When for example i choose in chopper to be commander or gunner, how do i switch between the two roles?

[OuedMeliz01]

change it in the editor, when you make double click on the chopper you can set (player as gunner, commander, driver.....)