You will need a 3 mm and a 5 mm hex wrench. A flat head screw driver. Some liquid soap or alcohol as lubricant.
Using flat head screw driver, pry off the end cap of left handle grip.
To take off the handle grip easily, need put some lubricant, such as liquid soap between the rubber grip and metal handlebar.
Then get some liquid soap or lubricant onto the screw driver, insert the screw driver between the rubber grip and handlebar. Then the rubber grip can be taken off. Then use 3 mm and 5 mm hex wrench to loosen the nut of shifter and brake lever.
When you replace brake lever,
Sometimes, if the brake cable is too tight, you may need loosen the 5 mm hex nut on the brake arm of the front brake.
Replace the grip lever. Tighten the hex nuts. Put on handle grip and end cap.