Find the Twitter application, and tap on it once to open the application
The Twitter application has a blue background with a white bird on it, with the word "Twitter" underneath it. Your Twitter application may be in a different position in this folder, therefore you will need to find it.
Tap on the box to the right of "Sound effects", which is the first option
This will turn the box blue and either add or remove a check mark depending on if the option is enabled or disabled. To disable the option, tap on the box to remove the check mark and make the box white.