Hello Barrie,
This is not really the place for such a question but I will try to answer your questions:
- if you go here you can find Prestashop 1.5.6. However, I doubt you need it.
- A full backup includes the files and the database. That is all you need to restore a shop. Your copy will initially use a different url. There are many places on the internet explaining how to adapt that.
- Note that you cannot run PS 1.5.6 and PS 9 under the same PHP version.
- Note that you will need to replace all modules.
- The Prestashop autoupgrade module often gives problems, specially over such a range of versions.
- It is probably a better option to use other software to handle the upgrade. You can use my free Copy_shopdata. On the Prestashop Addons shop you can find several paid options.
Success!
M