Remove roles from Sharepoint list item

void SetReadonly(SPListItem FinalizeItem, SPWeb web)

        {

            //void SetReadonly(SPListItem FinalizeItem)

            //SPFile file = Folder.Files[fileName];

            SPListItem item = FinalizeItem;

            string groupName = string.Empty;

            if (!item.HasUniqueRoleAssignments)

            {

                item.BreakRoleInheritance(true);

            }

            SPRoleAssignmentCollection SPRoleAssColn = item.RoleAssignments;

            for (int i = SPRoleAssColn.Count - 1; i >= 0; i--)

            {

                if (!(SPRoleAssColn[i].Member.Name.Equals("Viewers"))

                {

                    SPRoleAssColn.Remove(i);

                }

            }

            //item.RoleAssignments.Add(RoleAssignment);

            //item.Update();

        }