Hello, my name isXXXXX you so much for the question.
Your phone uses sound profiles rather than the traditional way of simply pressing 'up' on the volume keys.
Simply go to Menu >> Settings >> Profiles and edit whichever profile you prefer. You should see profiles such as 'normal', 'outdoors', 'silent' and so forth. Edit the one you want to edit and you should be able to adjust the volume for that specific profile. Once you've done that and saved your changes, you can then go back to profiles and SELECT that profile and make it active.
Let me know if you have further questions.
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