Add a group level
Microsoft Access adds a group header that contains an expand control and a record navigation section that contains a record navigation control. If you grouped on one field, Access moves the control on which you grouped to the group header. If you grouped on a table or query, Access moves all the controls ù including controls bound to fields that are in that table or query and controls bound to Lookup fields ù to the group header.
Remove a group level
Microsoft Access moves the controls in the selected group header and footer into the header and footer of the next lower group level.
Note To change a field that is used to group records, follow the steps to remove the group level, and then follow the steps to add a group level with the field you want.