You can upgrade it manually, do it on a test machine.
I have described in the german forum how to do it:
Instructions:
- Upload and upgrade the autoupgrade module to v4.15 -> Download from: https://github.com/PrestaShop/autoupgrade/pull/513
- Upload ZIP archive Prestashop8.0.0 to adminXXXXX/autoupgrade/download -> Download from (with xml-file): https://github.com/PrestaShop/PrestaShop/releases/tag/8.0.0
- Upload XML to adminXXXXX/autoupgrade/download
- Perform 1-click upgrade with expert function Update local archive
- select XML file and Prestashop ZIP file, enter version 8.0.0 -> update
Attention: looking for jsonDecode or Encode errors in section "Deprecations and removals":
This 2 console command fixes these errors (change module path):
find /path/to/modulefolder/modules -type f -exec sed -i 's/Tools:jsonEncode/json_encode/g' {} \;
find /path/to/modulefolder/modules -type f -exec sed -i 's/Tools::jsonDecode/json_decode/g' {} \;
for me the upgrade from 1.7.8.7 to 8.0.0 worked fine on a 1:1 test platform.