The battery on a Journey is located in the engine compartment, usually near the front of the vehicle. It's typically on one side or the other of where you would expect to find it - either directly behind your radiator, or just off to one side beneath some plastic coverings. The exact placement will vary depending on year and model, but generally speaking it should be easy enough to locate with a quick visual inspection. Once found, simply remove any fasteners that might be holding it in place and then carefully lift out the old battery before disconnecting its cables and installing a new one according to manufacturer instructions. Remember too that batteries can be heavy so take care when lifting them out as well as when connecting up their various terminals during installation!