To convert real data into a terrain height map you will need something called G16Ed - this can convert 8-bit greyscale bmp files into the G16 file format that you would need for an unreal editor heightmap.
I believe DGUnreal's site has a link to it but I am away from my usual desktop at the moment so I can't tell you for sure.
This does not, however, help you if you do not have the greyscale bitmaps in the first place. There are a variety of terrain viewing programmes available for free - they often use .dem file format so a quick google of dem viewer would be useful.
Please bear in mind that the dem files FREELY available for the area of the Eastern front are not of a useful scale at all and even the pay-per files are a bit too lo-res to be useful to an RO mapper.
One thing I did do was use Photoshop to trace the contour lines of an existing survey map and fill these lines on seperate layers with varying shades of grey. It actually worked quite well but is rather time-consuming and not recommended if you want to map the Caucasus mountains or somewhere.