Hi,
You can see how to do it here: http://www.battlefront.com/community/showthread.php?t=87942
And the text:
Campaign Game
* When a campaign scenario is updated, you can "import" your current progress from a saved game into the new scenario. Steps:
1. Update CMSF to v1.20.
2. Using v1.20 or later, save your current campaign between battles - from the point just after you dismiss the end-of-battle screen. Importing will not work for saves made at any other point.
3. From the main intro screen, start a New Campaign, and select the updated version of the campaign you want to use. HOLD DOWN THE SHIFT KEY as you click the OK button.
4. Immediately an "import" screen will appear. You'll see your saved game here. Select it, click OK, and then things proceed as normal. The game does the best it can to match battle history and core units from your saved game to the new version of the campaign, but if the author has made major changes then this will be difficult, so the whole process of importing works best when updates to the campaign are relatively small ones.