Let's do an easy answer: as far as I can remember if you're with a share hosting, you can't really. I did this trick for only one forum but it's very limited and the code is not fully finished yet.
I called my webhoster. I am not allowed to change the limit in mysql. Its is set to 4 there. In the XF-ACP have set it to 2. But this obviously does not have any influence because of the mysql settings.
Where do I find & enable the enhanced search and what is the benefit and downside over the normal search?
The modification of digitalpoint you mentioned, is it that one?:
If you can't change the mysql settings, I doubt you can install Java and Elasticsearch to run XF Enhanced Search. You'd have to move to a VPS account first.