The option to delete them is in the "Contacts" page.
Log onto your email account then click on "Contacts" in the menu bar. You should then see within the left hand column "Auto Complete".
Click on it and this will bring up a list of the contacts in the Auto Complete folder.
Select the contact you want to delete by ticking the box next to it then click on the "More" button in the menu bar and select "Delete". This will delete the contact from the Auto Complete section but will leave the contact in the Main section.
Check that the contact is not in your main list of contacts and if it is delete it then clear the history and cookies from your browser and log out of your email account then log back in and try the procedure outlined above again.