And sorry for the german, I hope you understand everything.
You need MorphMesh and OEdit. You may need FshEd too (more later)
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Get the xxxxx_loda.o file and the xxxx.fsh file (only if you don't have the bhed .bmp file) from a player you'd like to edit the headshape.

Open MorphMesh and select the first option in the process field. Open your loda.o file into the yellow area.

Now press on the dots next to the green area. Put in the name field a random name and press save.

Press Convert!
You'll now have a new file on your desktop (or whereever you saved it).

IF YOU DON'T HAVE A BHED .BMP FILE:
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Open FshEd and load your .fsh file.

Go to 'Object' -> 'Export' and fill in a random name again (don't forget the ".bmp") Save it.

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Now open your created .o file with Oedit. After you opened it, it will look like this:

Movement and Zoom of the previews in OEdit:
2d (the white ones) Zoom with ctrl + w. Move with ctrl + left mouse button
3d (the blue one) Zoom with the right mouse button , turn it with the left mouse button and move it like the 2d preview
...
Press 'Texture' -> 'Manage Textures' and load your bhed bmp file. Press OK

When your screen looks similar to this, you're ready to work.

It's pretty obivous how to edit the head now. Drag and drop the small spots on the 2d previews.
If you're happy with your preview, save it.
Mine looked like this:

Now open MorphMesh again. Select the second option.

Now load exactly the two files you loaded before in the same area.
This case "admorri_loda.o" in the first and your created .o file "ammo.o" file the second area. Press convert.
You can use your player_loda.o file ingame now. put it back in your player folder.
ingame preview:

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I hope i did not forget anything.
Feel free to ask something if you need.