Hi Mario,
It is pretty simple. Just get a copy of MathJax from https://www.mathjax.org/mathjax-v2-7-3-now-available/
I put mine in my servers html folder in a folder named mathjax.
In Moodle, go to Site administration > Plugins > Filters > MathJax. Change the MathJax URL to point to your servers MathJax. Test to make sure it is working. e.g. mine is currently https://10.0.6.202/mathjax/MathJax.js