How do I turn up/down the timer alarm volume on my Hotpoint BU71 double ove?

I have a Hotpoint BU71 double oven and it works very well. However, the timer alarm volume is very low and I can hear it only when I am in the kitchen near the oven itself. I have tried some combinations of button pushing, but without success. There are 6 buttons - the leftmost 4 are for timer and other functions, the rightmost 2 buttons are the + and - adjusters to time settings. Please advise. Thanks.