Hi Evy

If the new SCORM package has the same sco item identifiers in the imsmanifest.xml then the grades and tracking data won't change. 

If the package has modified indentifiers/added or removed scos from the package  any tracking data associated with the old sco identifiers are deleted as the grade could possibly change.

To check this you need to unzip the SCORM packages and view the file  imsmanifest.xml and compare the old and new files to see they are the same. If they are different then you need to edit the new SCORM package with your authoring tool so the items have the same name.

Then upload the new package to the existing SCORM activity and the grades and progress should be retained.

regards