Edit a DataGridView ComboBox Item.

Question

I need an editable combo (DropDownCombo style) appears on a DataGridView current cell. 
I tryed setting the column type as 'DataGridViewComboBoxColumn'. It works fine but I can't 
edit ComboBoxItems.   
How can I edit and insert new items direcly from combo ? Is it possible ?
There is any workaround to do ?
Thanks.
Brainjar.