To change your ShareID, select Account in the SpiderOak application running on your computer. Next to your current ShareID you will see a button which says Edit; press the button and change your ShareID as desired.
It is not possible to edit the "Name of Person Sharing" which appears at the top of each share. This will always by default display the name you gave when signing up for the account. If you absolutely need to change this information, you would need to open a new account.