Sorry for the newbie question, but I've added an autonumber field to my opportunity page, and while it works great assigning numbers to new opportunities, I can't for the life of me figure out how to retroactively have it number my existing records.  Any help would be appreciated.  Thanks very much!

Sorry for the newbie question, but I've added an autonumber field to my opportunity page, and while it works great assigning numbers to new opportunities, I can't for the life of me figure out how to retroactively have it number my existing records.  Any help would be appreciated.  Thanks very much!