Many aspects of the slideshow configuration were changed greatly between version 3 and version 4. This makes it difficult to transition an entire slideshow instantly from version 3 to version 4. However, one aspect of the slideshow configuration structure which was extended rather than revamped is the <galleries> section of the XML file, where all image galleries are defined. The result is that the image data from a version 3 slideshow can be easily transitioned to a version 4 slideshow.
As a side note, it should be noted that version 3 and version 4 of the extension are fully interoperable. It is not necessary to uninstall version 3 prior to installing version 4. In fact, you can use version 3 and 4 slideshows together on the same site (using them on the same page is not recommended).
To perform a slideshow data migration, first open the version 3 slideshow's XML configuration file. This can be done in Dreamweaver by selecting the slideshow in Design View and clicking Edit Manually in the Properties panel (Window > Properties). Then, return to the HTML page that holds your v3 slideshow. Place your cursor next to the v3 slideshow and run the v4 Insert Wizard. Don't spend time configuring the slideshow yet - just add a single empty gallery, then save and exit. Still in your HTML page, select the newly-inserted v4 slideshow and click the Edit Manually... button in the Properties panel to open its XML configuration file as well.
You should now have the v3 and v4 configuration files open side by side. Near the bottom of the v3 file, locate the <galleries ... > ... </galleries> section, which will appear something like this, with one or more <gallery> child nodes:
Copy this code (including <galleries ... > and </galleries> !) and switch to the v4 configuration file. Locate the corresponding <galleries ... > ... </galleries> section at the bottom of the v4 file and replace it with the contents you copied from the v3 file. Save your change and close both configuration files.
Now that the gallery and image data has been migrated to the version 4 slideshow, you can switch back to the HTML page and launch the edit wizard for the version 4 slideshow. (If you receive XML parsing errors, close the edit wizard, re-open the v4 configuration file, and make sure you didn't make any errors when replacing the code.) You can now configure and customize the slideshow as desired; all of the migrated galleries should appear in the Image Galleries tab. You can customize the migrated images with version-4-specific options as well.
Important: Once you're ready to remove the old version 3 slideshow, be sure to also remove any and all <script src="v3flashslideshow/slideshow.js" ... ></script> file references from your file to prevent conflicts. Failing to do this may could cause version 4 slideshows to not appear properly.
Important Note: The format for the autoplayDelay attribute changed between version 3 and 4. If your copied v3 slideshow code included a <gallery ... autoplayDelay="..." ... > value, remove it and then re-create your autoplay delay in the Global Config / Playback Settings section of the main wizard.