Yashica is a company that designed, manufactured and sold lenses to work on other companys' camera bodies. If you owned a Canon camera, you would buy a lens that was built with a Canon mount. Since the lenses were manual focus, the concept was that other than the specific mounting bracket, the lens was essentially the same. Yashica lenses were generally less expensive than those made by the original equipment manufacturer and could be purchased in a variety of focal lengths from wide angle up to telephoto. The company produced zoom and prime non-zoom lenses.
Hold the Yashica lens in your hand and begin removing the small Phillips screws located on the exterior of the lens. Depending on the type of lens you are working with, the number and location of the screws may vary. However, generally the screws are located near the front of lens just inside the front lip of the lens housing. You will also find screws on the sides of lenses. Some models may require you to peel back or remove the grip material around the focusing ring.
Remove the screws from the rear mounting bracket of the lens. With the front and side screws removed, the mounting bracket is the last component holding the lens together. When you remove these screws, the lens could easily fall apart. For that reason, remove the mounting bracket while the lens is resting on your work table.
Carefully pry the lens open. The mounting bracket and front element of the lens will be released allowing you to view inside of the lens compartment. Inside you will see a series of glass lenses grouped together. These are lens elements, and the number and size will vary depending on the size and type of the lens.
Remove the screws or locking ring that keep the barrel of the lens together. Pry the two sections of the lens barrel apart. From here you will be able to remove all the internal glass lenses and focusing mechanism.