Hello! We are truly sorry for your delayed response and thank you for using Opera's Services.
Refer to this Facebook Article: https://www.facebook.com/help/204306713029340/
After that, delete that Account associated with your old Opera account and link it to your new one. You should be able to add your Facebook account to your Opera account.
Thanks! Please post back if you have any further issues
I also have the same problem & would like to update my opera password to make it more security-wise! Could someone in opera help us please? E-mail is penelope.sue(at)live.ca - Thank you in advance for your timely response.