If East is replaced by West, then South-West will be replaced by:

In standard directions, East and West are opposite to each other. If East is replaced by West, it means the directions are rotated by $180^{\circ }$ (or completely inverted).
To find what replaces South-West, we look at the direction exactly opposite ($180^{\circ }$ rotation) to South-West:

* Opposite of South is North.
* Opposite of West is East.

Therefore, South-West will be replaced by North-East.