If your are wanting to make your CB radio sound more louder and more clear, then increasing the modulation, which is know as swing, can make that happen. There are two ways to increase your CB radios modulation, the first way would be to add a good quality power microphone. A power microphone, has a built in amplifier circuit, that amplifies your voice, making it sound more louder and clear. Most power microphones are powered by a 9 volt battery, so if you use your CB radio daily, you might need to change the battery frequently because if you continue to use your power microphone with a dead battery, your microphone will not perform at its best.
The second way to increase the modulation on a CB radio, would be to dissemble your rig and adjust the modulation pot. Most manufacturers install a modulation pot into CB radios, so you and peak and tune it, to gain more swing. To locate were the modulation pot is located on your rig, you will have to look at the manfacturers service manual.
If you are wanting to increase the modulation on your CB radio, then below is a excellent video that shows a quick tutorial on how to do so: