1) how to clean the injectors on a '87 mercedes 300td? 2)How to change the glow plugs?

The injectors must be serviced by a diesel tech, there is a special test rig needed to re set pintal break off pressures and to check for leaks ands test the spray pattern, get this wrong and you will have major problems, the glow plugs a will unscrew after you remove the electrical wire or buz bar if used, they are a conventional R/H thread, you may have to work then in and out a little to break up any carbon on the bottom of the thread's, but they should come out quite easily.