Just to be clear, there is a jack (the device used to lift up the vehicle) and a jack stand (a stand that can hold the weight of part of the vehicle after using the jack to lift it). It is safe to change a flat using the jack that came with the car; that’s what it’s designed for. It won’t be the simplest jack to use and definitely not the highest quality, but it will get the job done. For your own safety, do not go under the vehicle while it’s supported by the jack.