Katherine it depends more on if you change the length of the shafts, if you are staying the same length then you probably do not need to change the weights unless you want the head (swingweight) to feel heavier or lighter.
Of course this depends on the balance point of the new shaft but if you stick with the same shaft in a softer flex it shouldn't be too much different.

Hi Matthew and thank you so much for replying. I was thinking I would also have them reduced in length by an inch. My feeling is that I need a softer shaft for getting better launch and “feel”; and a shorter shaft for “manageability”. Would I need to change weights if I did that do you think?

Katherine, following are the changes resulting for different changes in club specs:

(1) +/- 1/2 inch in club Length = +/- 3 swing weight points
(2) +/- 5 grams in grip weight = -/+ 1 swing weight point
(3) +/- 2 grams in head weight = +/- 1 swing weight point
(4) +/- 9 grams in shaft weight - +/- 1 swing weight point- will be a variance depending upon the distribution
of weight within the shaft

Also +1/- 1/2 inch in club length changes the playing lie +/- one degree

So for example if your choice of shaft were 9 grams lighter and 1/2 inch shorter the swing weight would go down one swing weight point for the shaft change and 3 swing weight points for the decrease in length. Being down 4 swing weight points you could add 8 grams to the head or 6 grams to the head and a 10 gram lighter grip to get back to your original swing weight. Hope this helps.

Katherine, following are the changes resulting for different changes in club specs:

(1) +/- 1/2 inch in club Length = +/- 3 swing weight points
(2) +/- 5 grams in grip weight = -/+ 1 swing weight point
(3) +/- 2 grams in head weight = +/- 1 swing weight point
(4) +/- 9 grams in shaft weight - +/- 1 swing weight point- will be a variance depending upon the distribution
of weight within the shaft

Also +1/- 1/2 inch in club length changes the playing lie +/- one degree

So for example if your choice of shaft were 9 grams lighter and 1/2 inch shorter the swing weight would go down one swing weight point for the shaft change and 3 swing weight points for the decrease in length. Being down 4 swing weight points you could add 8 grams to the head or 6 grams to the head and a 10 gram lighter grip to get back to your original swing weight. Hope this helps.