raster - Reclassify in QGIS

I have a raster file (DEM) whose values range from 0 to 1565 meters (elevation). I want to extract a new raster file after classifying the values in four classes like this:

<= to 150 meters
150-600 meters
600-900 meters
>900 meters

after that I want to make statistical calculations.

How can I do this in QGIS?

I have installed the LecoS plugin and I probably don't have the NumPy, SciPy, Pip libraries installed, because it doesn't work.

• How can I see if I have these libraries?


• How do I install these libraries, if I don't have them?


• Is there an easiest way to extract a classified raster file?

I have Windows 7 Pro (64-bit) and QGIS 2.18.7