Reclassifying raster layer with certain colors for value ranges in QGIS?

You may apply a reclassification by right-clicking on the layer in the Layers Panel and then clicking on Properties: from the dialog that appears, go to Style and then set these parameters (you can adapt them following your specific needs):

Please note that in step No.5 you set Equal interval as Mode, but you only do this for the possibility of editing the number of classes (actually, you may choose a different threshold for different categories, even if the Equal interval is set).

Finally, click the Apply button for applying the changes.

Instead, if you want to create a reclassification on a new file, you may use several tools from the Processing Toolbox (as an example, the Reclassify values SAGA tool or the r.reclass GRASS module) or directly using the Raster Calculator from the Raster Menu.

• Go to Layer Properties-->Style menu
• Choose Render Type-->SingleBand Pseudocolor
• In the classes' field enter 6 and press Classify
• In the table on the left change the values and colors as needed.