Which path to upgrade from Mac OS X 10.6 (10A432)? In my "old" Mac mini I substituted the HDD with an SDD and added more RAM.

I reinstalled Mac OS from the only CD I actually have, version 10.6 (I think it's Snow Leopard, has a version code '10A432'.

I tried to upgrade directly to the latest Mac OS High Sierra 10.13, but it failed, my system hangs while finishing installation after first or second reboot. 

Official Tech Specs


https://support.apple.com/kb/SP577?viewlocale=en_US&amp;locale=en_US


Model Info


Part Number: MC238T/A
Model Number: A1283
Mac Mini 2.26/2X1G/160/SD/AP/BT - ITA


SW information


Mac OS X 10.6 (10A432)
Kernel Darwin 10.0.0


Questions


What's the maximum jump I can do in a single step?
Where can I legally download (and buy if needed) the DVD with the needed OS version?
You most probably have this model which can be upgraded to 10.11. 

Apple has a support article describing the steps required to upgrade from 10.6.8 to 10.11. Basically you update up to 10.6.8 and then get the installer from the App Store.