New forms:
Generate a new help project - make sure to use the same Help Project name and have all settings as in the original project
The new forms are automatically copied to the current (existing) project folder and linked in the content tree below the Dialogs node.
Changed forms:
All changes wil need to be done manually. If changes are large then you may consider replacing the old HTML file with the new one ( Update using Take Screenshot tool ) and copy texts from the old page into the new.