Can I download Elementary OS for free?

Everything by Elementary is free and open source. The developers are committed to bringing you applications that respect your privacy, hence the vetting process required for an app’s entry into the AppCenter. All around a solid distro.

How do I switch from Ubuntu to elementary OS?

You can switch to one of the others fairly easily, just by installing one of those and removing ubuntu-desktop and the applications it bundles. The systems underneath these packages are exactly the same. It’s Ubuntu. Netrunner and Elementary OS are different distributions run by different people.