Well.. Let me try to Help...
Step 1: Go to "Public Profile" after you have logged in PW.
Step 2: Click on "User Control Panel" on Top Right Hand Side of the page.
Step 3: Click on "Edit Your Details" on Top Left Side of the page.
Step 4: Update you Date of Birth details via dropdown fields.
Step 5: Click "Save Changes" at the bottom of the same page.
Hopefully this would do it