When dealing with this myself, I started here:
then - in about the middle of that page, reading about DirectXMath:
It's pretty much just including the right header files and changing "D3DX" prefixes to "XM". Not quite that simple, but that's the general idea.
Your first program will probably have inclusions/usings like this:
#include <d3d11.h>
#include “DirectXMath.h”
#include “DirectXPackedVector.h”
using namespace DirectX;
using namespace DirectX::PackedVector;
struct mystruct
{
DirectX::XMFLOAT3 position;
DirectX::PackedVector::HALF packedValue;
};
Of course, it's not considered best practice to have "using namespace", but in this one instance I found that "DirectX::" on every line of my program was making my program almost impossible (for me) to read - so I went with the "using".
Good luck!