If you only have 10 items use the Large function to subtract the 4 largest
Exapmle data in cells A3:J3
=(SUM(A3:J3)-LARGE(A3:J3,1)-LARGE(A3:J3,2)-LARGE(A3:J3,3)-LARGE(A3:J3,4))/6
if the number of cells floats use the Small function to get the six smallest
=(SMALL(A3:J3,1)+SMALL(A3:J3,2)+SMALL(A3:J3,3)+SMALL(A3:J3,4)+SMALL(A3:J3,5)+SMALL(A3:J3,6))/6