How to level concrete surface?
The way you mentioned is usually the correct way to go, as long as the settlement was not only developing recently. You might want to find some self-leveling concrete product. An example would be the Rapid Set CTS concrete leveler (in US). 

Please do follow the manufacture's instructions, especially about properly preparing the old concrete surface so that the nearly poured concrete could bound well with your existing surface.

If your settlement started recently, it would be better to figure out the cause before repairing. For example, examine if there is any water leak that could washout your soil.