You can no longer edit cheque # list under SUMMARY PAGE – ACCOUNT – EDIT.
To add a new item in an account register, click into the Cheque # field and type in the new item., it will be added to the dropdown.
To remove an item from the dropdown all instance where the item has been used must be removed or changed to something else. Find and Replace extension can help with this. Once the last instance is removed it will disappear from the dropdown.