If you don’t know How To Change Email On Facebook on desktop then follow these steps:-
1. Access Facebook, click the down arrow, and scroll to Settings & Privacy.
2. Select Settings, and click Accounts Center. 
3. Select Personal Details, then Contact Information, and then Add New Contact.
4. Select Add email address, enter your email, select a Facebook account, and tap Next.
5. To delete an email, select it, tap Delete email address, and click on the Delete button to confirm. 
6. A verification code will be sent to your email address; enter it and tap Next.