You can switch between aircraft by going to the Profile tab and selecting “My Hangar”. You’ll get a list of airplanes and you can select the aircraft and then there’s a row of choices, one of which allows you to choose from the list of liveries for that plane.
The only way to switch between planes once you are flying in the sim is if you are in Developer mode, which means your flight is not being recorded in you Pilot’s log.
As noted above, the planes are not locked to challenges.
You can find a good list for what you get with each of the Standard, Deluxe, and Premium packages here:
Had to go to the Wayback machine to get this list, sad they removed it from the regular wiki page.
Hello,
Welcome to the forums! If you would like help from the community, the best place to ask is the Community Support category. Your thread has been moved there.