You change the objetct group.
But take care if the same object group is usesd in multiple ACLs then this will add or delete in all the ACLs.
Reference:
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a00800d641d.shtml
example:
(config)# object-group network host_grp_2
(config-network)# network-object host 172.16.10.1
(config-network)# network-object host 172.16.10.2
(config-network)# no network-object host 172.16.10.2
(config-network)# exit
sincerely
Patrick
