Need help with Nelson Reed 1204 Active Crossover

Nelson Reed is no longer in business. I have their 1204 active crossover which needs to be converted from crossing over at 80hz to crossing over at 40hz. I don't have a schematic and am frankly not well versed in circuitry, but fairly skilled with a soldering iron when pointed in the right direction. Is there anyone who can help?

Am planning on getting a digital camera soon and would be able to post or email a photo of the board.

Thanks, in advance.