Question: how to change your birthday on facebook even when it's limit reached?
Answer: #1: Go to your profile and click Update Info on your cover photo.
#2: Click Contact and Basic Info.
#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)
#4: Use the dropdown menus to change your birthday.
#5: Click Save Changes.