The speed of your E-bike depends on how hard you pedal, the mode you are riding in, and is limited by regulations in your country.
In Europe and Australia, an E-bike must have a motor with a maximum power of 250W, assisting the E-Bike to a maximum speed of 25 km/h. In the US, the rules are different. There, E-bike motors can have a max of 500W and assist up to 20MPH (32km/ph) or more.
All Giant and Liv's e-bikes imported and sold through authorised retailers in Australia are pedal-assist limited to 25 km/h in accordance with Australian regulations (EN15194); there is no motor support above this speed.
If the pedal support still functions above these limitations, then the bike becomes a so-called speed pedelec.
While you are pedalling, the E-bike motor will assist you until you reach these maximum speeds. Once you reach these maximums, you can go faster, but your legs will have to do all the work; the motor will no longer provide assistance. Once your speed drops below the maximum speed, the motor assist will resume.