Changing Zinc acetate dihydrate to Zinc acetate
Wikipedia is your friend...Zinc Acetate


  
    Decomposes at 237 °C (459 °F; 510 K)
    (dihydrate loses water at 100 °C)
  


So heating to 120-130 °C for several hours would remove the water, but not be hot enough to decompose the salt. The dried salt will be hygroscopic of course so store it in a desiccator.