shopware Upgrade from version 3 to 5.2

Thanks alot

It seems I am unlucky! my shopware version is 3.5.5

However I went through the instructions you suggested and went fine until the upgrade step which didn’t work and this message was displayed:

“The database update does not support Shopware version 3.5.5.”

So what should I do to to have my website and contents back in  newest shopware ??