Upgrade Possiblity When Checking In On Line

I have recently joined V-Flyer & am very green so please forgive me if this question has been answered before. If I check in on line tomorrow (Mon 26/6/06) for my flight to Miami on Tuesday out of Heathrow is there less likelihood of me being upgraded? Would it be more advisable to check in in person?I have a full flexible ticket & am travelling in PE & am a silver member? Any prompt answers would be much appreciated, thanks.Roxy-Popsy.