The information that you provided during sign up will automatically default into the Account Details fields.
If you want to make changes to this information, just click in the field and delete the current entry. Make the changes you want and then click the Save Changes button at the bottom of the tab.
Changes can be made in all of the fields, except for the eHive ID field. All of the fields in Account Details are mandatory and you will not be able to save changes if information is missing.