Changing volume on icn 520

Could anyone help. Is it possible to change the volume on icn 520. When driving you can hardly hear what is being said. I wondered if you can change this by using a program on the pc to increase then transfer back to the navman. Or am I trying to be a little ambitious.

Many thanks

i use the navman icn 520 and also find it a little on the quiet side. i also drive a truck so find that it also makes it harder to hear, but i have overcome the problem by buying a small pair of amplified spekers for use with a personal stereo, and plugged them into the headphone socket. now i have plenty of volume