Cs-Cart Upgrade 3.0.6 to 4.7.3

Hello. I need help upgrading a website form a client. It has now the version 3.6 and I need to upgrade it to 4.7.3. There is an add-on for free that can help you to do that. You have to install first the new website and install the plugin (Site Importer) after that you add the root directory from your old website to the site importer add-on and the plugin will do the job for you. Now the problem that I'm having it may be two things. I'm not typing the correct directory because I'm not good at this things or the add-on is not detecting the old website because is running a different php version. Im not able to have both sites runing right if I change the php to the new version the new website works and the old stop working and if I down grade the php the old website work and the new website stops woring. According to the support from the cs-cart it has to work but no luck at all. The old website has about 700 Products I need to bring all of them exactly they way they are to the new website. There are other way that show how to do it but I dont want to risk and deleted the old site and losse all the prodcuts. Thank you.