forgot password

I purchased my xbox on line and have been using the profile already on it and was granted permission by owner of account, I have added a prepaid card on the account but now it is asking me to sign in but I do not have the password and all the information on the account matches the previous account holder who has moved out of state. How do I get back into the account and can I reset the password so I will not lose all the games that were  bought on this account? Can you help?