If you use a Xbox controller, press the small play (right one) button, then scroll along to garage on that menu and change cars
Other tips, when you get to a radar that will reveal hidden cars on the map, in the map use the buttons above the accelerator and brake (controller) to change map filter to exploration to see there locations
If you want to access crew and friends press the right analogue stick down, you can then add friends to the crew, change crew master etc
When you have a crew this stays even when you disconnect, very useful if you tend to play with the same people
Other tips, when you get to a radar that will reveal hidden cars on the map, in the map use the buttons above the accelerator and brake (controller) to change map filter to exploration to see there locations
If you want to access crew and friends press the right analogue stick down, you can then add friends to the crew, change crew master etc
When you have a crew this stays even when you disconnect, very useful if you tend to play with the same people