Open the Facebook app or go to Facebook in a web browser
Log in to your account
Tap the menu icon or profile picture
Go to Settings and privacy
Select Settings
Open Accounts Center
Tap Personal details
Select Contact info
Choose your current phone number
Tap Remove phone number or Edit phone number
Enter the new phone number
Save the changes
Enter the verification code sent to your new phone number
Confirm the new phone number
Remove the old phone number if it is still listed