How do I change the fuel filter on my 1980 Mercedes 300CD?

It's a pretty easy job. There are 2 of them first of all. The prefilter is in the fuel line ( look below the inj. pump ). It's held in place by clamps so undue the clamps and replace the filter ( it's hard to screw up because the filter is an L-shape but I'll say it anyway, there should be an arrow on the filter which indicates the fuel flow direction ). The main one just unscrews ( very much like a spin-on oil filter ). You will get some diesel fuel leaking out so you may want to put some rags or paper towels underneath to catch the fuel just to keep the smell down.