Can't get my plugins running with the migration from 4.2 to 4.3

In my shop in version 4.2 there are some extra plugins installed. In the documentation it says that I have to delete all files except of the dataSettings.json and plugins.json file. So this deletes also all the plugins content in the Plugins folder.
Now I have the new version running without the extra plugins. When I copy the new and old ones to the new plugin folder and updated the plugins.json file, it doesn’t show in the Configuration > local plugins.
What is the correct method to get the plugins working as they where on the old version?

NMS wrote:
You need to have Pluigns built for version v4.3
In almost all cases you cannot just use a v4.2 plugin and change the plugins.json file

Are the plugins you wan to use for v4.3 available in the marketplace ?
If not maybe you need to contact the developer

Thank for the info!
The problem was the SevenSpikes JCarousel plugin that had a version 4.31, but was installed as 4.3 which gave all kinds of problems.