Hello Guys and Gals!
To get this achievement, you will first need to complete the F2 career mode series which shouldn't take too long (Half an hour if that).
Once that is done, your agent (Who seems like such a bitch btw) will give you a choice of teams. For me, as i won the F2 championship, i was able to pick who i wanted.. So for this one, all you need to do is either pick Mclaren or Alfa Romeo (Sauber) to unlock it!
The other way you can unlock it is if your winning a lot during your career and the teams rep goes up, you will eventually be offered a new contract by your team.. You can either accept that or theres an option to "Negotiate with a different team" Click that and choose one of these teams to unlock.