There is no good way .... any way you convert Hilton points to Delta miles, you lose most of the value. The Hilton site indicates you can convert 10K Hilton points into 1K Delta miles .... not a good value! I don't know any better ratio doing a straight conversion of Hilton points from your Hilton account to Delta miles in your Delta account.
However, if you have enough Hilton points for a hotel reservation/s, you probably can do better trading on Coupon Connection forum here.
You should be able to trade at 2-3 Hilton points for 1 Delta airmile; i.e. a 50-75K Hilton point reservation for a 25K Delta flight reservation, etc.
Good luck!