I would give the whole plant (the above-ground part) a scrub with a toothbrush and soapy water, using a gentle sideways brushing motion to remove the scale insects. The important thing is to remove them, they are no longer mobile when they are mature. Rinse the plant well the next time you water. Then follow up with a 70% alcohol spray (in the shade only) every week or so after that, to catch any bugs that return. Just hit all the surfaces of the plant (above-ground parts) with a fine mist of alcohol and let the stuff evaporate in the shade.
That will give you a nice clean plant. In the meantime I would recommend treating the plant with a systemic insecticide (I use imidacloprid, available under various brand names). You water the product into the soil, the plant takes it up through the roots, and a few weeks later it becomes toxic to any remaining bugs who try to eat it. Follow the instructions on the label. It's important the plant be awake and active (not in some degree of winter dormancy) for a systemic to be taken up efficiently. It's important to use the right amount and properly saturate the soil for it to work right.
Also see this thread:
The thread "Succulent Pests & Diseases" in
Cactus and Succulents forum
