Facebook Account recovery

Hello,
I created fb account a year ago on phone number ...My account is still WD me cz I didn't log out from there..The problem is that from last 4 months my number which I used to create fb account has been off and I recently came to know someone else is using that number ..I don't even remember password of that account how can I get the new password I am already using that account but I want to change that number help?