OpenCart – Re-install version 3

I am running a small website with 59 books for sale
The shop is here:
http://mouritz.co.uk/shop/
A few months ago I hired a PPH (expert!) to upgrade OpenCart to 3.0.0.0, but it is not working properly. E.g. there are no email notifications. I have tried to install OpenCart on a different site, and then the email notifications work alright, so it is not a problem with OpenCart. The re-installment needs to maintain all existing information, e.g. orders, customers, products and postal charges (weight based for different areas).
Payment: Paypal
To be completed within 3 days please. The existing Open Cart is still functional.

The existing theme is an Open Cart default theme. The following extensions are installed but they are all easy to replace in case they do not work after updating: Export/Import Tool for OpenCart 2.0.x; Import/Export CSV ; Local copy OCMOD ; Remove Affiliate ; UltraImageManager.

Please do not phone or email me directly. Use only PPH for correspondence.