Step 1: Go to your profile and click About on your cover photo or you click here
Step 2: Click Contact and Basic Info
Step 3: Scroll down and click Edit next to Birth Date or Birth Year (you’ll need to hover over the info you want to edit for the Edit option to appear)
Step 4: Use the dropdown menus to change your birthday
Step 5: Click Save Changes.
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You can change who can see your birthday by adjusting the audience. There are 2 audience selectors next to your birthday: one for the day and month and one for the year. Friends won’t get a notification about your upcoming birthday if you don’t share the day and month with them.
Having Problem changing your birthday?
Facebook wants everyone using their service to provide their authentic name, information as well as birthday, so users of the network will always know who there’re connecting with. Because of this, you can only change your birthday a limited number of times.
If you just recently changed your birthday on Facebook, you may have to wait a few days or months before you can change it again. Good luck… Please share this guide!!!