What is different about it and how do I turn it on?

According to BelannaerTV (see vid here), who looked into the code of Cities Skylines, in combinations with my own findings the effects of Hard mode are:

1. Building and maintenance cost 25% more compared to normal.
2. Relocation cost are 50% of the construction cost instead of 20%.
3. Refund on buildings/roads is reduced to 50% instead of 75%.
4. Residential/Commerial/Industrial demand is reduced by 20 points. This results in less city growth.
5. Buildings level up more slowly, (see video for details).

Hard mode can be enabled by enabling the hard mode mod in the Content manager. This mod is installed by default.

Thanks for the reply.

I am playing on console, so looks like I cannot access this mode.