Depends, are you talking about ringtone volume? If so, you can do this through Menu/Settings/Call settings.
If you're talking about voice volume, usually, the Vol + & - toggle on the side of the phone.
I will assume you have this toggle? I don't have a Samsung Galaxy, but usually, they're all located on the right or left side of the phone, but I believe it will be on the left side (not on the front face)
Volume question: Nexus Galaxy. The max volume on my new phone isn't very high. When I play back audio and set the volume to the Max it still isn't loud enough to hear without putting the phone near your ear. Is there a way to increase this, or is it just the nature of the beast?