Hello,

Thank you for your post.

Yes, you can update from 1.8a to 1.9 (or any other version) by applying the updates one by one in the correct order until you reach the version you desire. Unfortunately you cannot use 1.8c to 1.9 update only because the updates are not cumulative. You will find the details on update procedure in the update instruction file.

If you are more experienced user and need the update to be done on several pages, you can also easily make your own cumulative update by combining the files and Query scripts from the updates together (overwrite older updates files by newer ones).

I would strongly recommend you to backup your web and database while doing such a complex update to avoid loosing the data.

Best regards