As Joey P stated, on the stem of one of the knobs there should be either a small slot or a small hole. Stick something (a straightened paper clip will work) into the hole while pulling gently on the knob.
Once the knob moves slightly, pull the paper clip out and the knob should then slide off, then pry the decorative cover off, underneath that you will find the screws.
After you’ve removed the screws and the latch mechanism, remove the screws in the latch bolt (on the edge of the door) and slide that out.
At this point you should have a large hole in the door and a smaller hole in the edge of the door. If so, you’re golden. 
Simply install the deadbolt as per the instructions. 
