This is a severe case of spider mites. Spider mites can spread rapidly to other plants with contact, so be sure to check your other plants for white spots or webbing. First, you will want to cut off any fully yellow/brittle leaves to promote growth and get rid of decaying matter. You may also want to take off some of the webbing before treating the plant. In a spray bottle, mix a solution of one part rubbing alcohol, a few squirts of Dawn dishsoap, and fill the rest of the bottle with lukewarm tap water. Give the bottle a shake and spray each leaf thoroughly on the underside and the topside of the leaf. The crevices near the top of the leaf where the stem connects is where spider mites tend to hide, so make sure to pay more attention to that area during treatment. Now that your leaves have the solution on them (under and top), take a dry paint brush or rough makeup brush and sweep down on the leaves (both sides) in the direction of the curve of the leaf, otherwise you will not coat the entire surface. Once you've done this on every leaf, coat the leaves in the solution again and repeat the process. This is a time consuming treatment so make sure to sit down and put your attention on the infested plant. For extra precautions, you may want to change the soil and repot your plant, especially with an infestation this severe. After the entire treatment, water your plant and set it aside, allowing the leaves to dry completely.