In the Friedman's book: Algebraic Surfaces and Holomorphic Vector Bundle , there is concept elementary modification at Ch2 Def15.
Let V is rank 2 bundle on X and L a line bundle on effective divisor D, W is elementary modification of V, if we have exact sequence: 0$\to$W$\to$V$\to$j$_*$L$\to$0
How to understand the elementary modification? If W is elementary modification of V, how to get V$^\vee$ is obtained as an elementary modification of W$^\vee$?