I have now prospect hd v4 and my upgrade to Neo is for free but my question is can I upgrade to Neo Hd or Neo Hd 4K for free

You can check on the CF website, but they have been giving the free upgrade to Neo4K v.5 to PHD v.4 customers.
That's what I did.

The code they will send you will be for 4K ... It won't work with HD.

Thanks Guys