Short answer: Assuming you're shooting in aperture priority mode, fiddling with the shutter speed or ISO actually won't change much.
The exposure is automatically calculated by the camera for you and it tries to estimate what shutter speed + ISO will give you a correctly exposed photo. Assuming you're not happy with what you see after you take a photo using your chosen aperture, your next step if you stay in that mode is to tweak the exposure compensation value (EV) upwards if you want brighter photos, or downwards if you want darker photos. If you change the ISO, what will happen if you don't change the EV value is the camera will most likely change the shutter speed to compensate for you changing the ISO, and vice versa, if you change the shutter speed, then the camera will tweak the ISO. If you're manually setting all three, well that's no longer really aperture priority mode. Anyways, onto the messing with the EV settings.
I don't own that camera, so I can't give you an exact step by step, but a quick search tells me that the camera has EV compensation, which means you can change the value. It will probably look something like this, and it will probably pop up somewhere on your display when you take photos.
-3 | | | -2 | | | -1 | | | 0 | | | 1 | | | 2 | | | 3
^
The ^ shows you what the camera is aiming for, and you should be able to tweak that higher or lower. For example
-3 | | | -2 | | | -1 | | | 0 | | | 1 | | | 2 | | | 3
^
will make your photo brighter, so your ISO will go up or shutter speed down, or a mixture of both.
-3 | | | -2 | | | -1 | | | 0 | | | 1 | | | 2 | | | 3
^
will make your photo darker, and your ISO will go down or shutter speed up, or a mixture of both.
