Turntables can accept may different cartridges, with differing qualities, and some are more expensive than others. The important thing to remember when replacing the cartridge is to compensate for weight. The arm and needle need to be balanced. If the new cartridge is of a different weight than the existing cartridge, you will need to make adjustments. The turntable comes with weights that can be used to compensate.
Remove the existing cartridge. Undo the two screws on either side of the top of the shell. The shell is the cartridge holder at the end of the arm. Pull the lead wires carefully off the existing cartridge. Separate the shell weight from the old cartridge if there is a shell weight. The shell weight is the rectangular piece that is inserted between the shell and the cartridge. Take out the stylus weight if there is one present -- the stylus weight will be the larger screw between the two cartridge screws on the shell. You should end up with a set of parts: One stylus weight, two screws for the cartridge, a shell weight, and a cartridge with a stylus attached (the stylus is the needle).
Check the replacement cartridge weight. On certain Technics turntables, the shell weight is used if the cartridge is between 3.5 and 6.5 grams. If the new cartridge is more than that, the weight isn't needed. Your turntable may have different requirements.
Attach the cartridge to the shell with or without the shell weight. Slide the existing stylus on. Use the existing screws and don't over-tighten. Fit the overhang gauge to the shell -- it clips on. Adjust the overhang. The stylus tip should line up with the end of the gauge. Make sure the cartridge is parallel to the shell. Slide the electrical connectors onto the new cartridge. Tighten the screws and remove the gauge. Discard the existing cartridge.
Only add the stylus weight after adjusting stylus pressure. Use the stylus weight to add pressure if necessary. You will need more pressure for scratch play. The stylus weight adds 4 grams on a Technics turntable.
If weights are missing, you may have to purchase replacements.