Follow the tutorial carefully .. its all in there ...

Like Mak. said there is an option to set the colour for each height and while there you can play a bit with the scale and alter the global height of your map ..

from the tutorial;
Spoiler Alert, click show to read: 
Open the color scale box at the top of the screen and select modify scale. Go through the pallete and change the color scale to a black and white. Its a fairly simple process and only requires a little bit of algebra. Modifying the pallette is also important for creating different elevation effects and playing around with it can help create good maps. You will also see an altitude range. The altitude range specifies the altitude of the area and will be reset to the area's range of altitude every time you load data. In order to create a continous map, modify this so its constant for the places you will connect together. After this, close that box and then open the Geo Coordinates pull down and turn the coordinates off. From there go to File and save map image. Save it as any image file you like.

https://forums.totalwar.org/vb/showthread.php?t=57828


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