Production Manager > Job Properties > Color Management Tab > Dither (Choose One) > Edit
The lower the frequency, the lower the LPI (Lines Per Inch). The lower the LPI, the larger are the halftone dots but the less the tendency to show banding. The higher the LPI, the smaller the halftone dots but the greater the tendency to show banding. Reduce the LPI for each color and test print. Stop when you're happy with the results.