Thanks for reaching out. It's no longer possible to convert a standard account to an education account. You will need to sign up using a different email address, or you will need to first edit the email address for the current account to a backup email.
You can change the email address by clicking the Account Settings link from the drop down in the top right corner. Then click on Manage Account on the left side of the screen. Once you change the email you will be able to sign up for Education here.
