Synthetic Oil for 2002 Ford Focus on 2002 Ford Focus

Can I use Synthetic Motor Oil in my 2002 Ford Focus? If I can....if I ever needed to can I switch back to conventional oil I heard that you cannot. Also, I have heard many miles should I wait to change my Synthetic oil.

Asked by for the 2002 Ford Focus
10,000 on a Group I POE; 5,000 - 7,500 on a Group II PAO