The word "decreased the volume" means to lower the sound or reduce the intensity of something. However, there are a number of antonyms that indicate an increase in volume or intensity. These include "amplify," "boost," "raise," "intensify," "augment," "magnify," and "heighten." If you want to make something louder or more intense, using these antonyms can help you convey the desired message. Using opposite words in writing or speech can add depth to the meaning and make it more vibrant. So, next time try using antonyms of "decreased the volume" to communicate the whole meaning of the sentence.