Hi ccristian,
My "guide" is for upgrade from older Prestashops like 1.6... and yes, uninstall all modules (most of them won't work correctly in 8x, or won't work at all). For the demo products - it doesn't matter, when You copy old base over the new one, it will replace it.
added: Pay attention to the version of php, 1.6 work on php 7.0, so start 1 click.. on php7.0 or 7.1
If Your version is 1.7x You just use point 7