If your Z-Axis threaded rods are loose upon delivery you may need to re-align them and tighten the 2 grub screws that secure the threaded rods to the blue couplers.
Once you have secured the threaded rod to the blue coupler you will be able to turn that rod by hand in order to raise or lower that side of the X-Axis assembly. Your machine should be OFF when you do this as the power going to your stepper motors might make this difficult if your machine is ON. You should move (turn with your fingers) your Z-Axis threaded rods up/down in order to correct the levelness of your X-Axis rods (the X-Axis rods hold your extruder carriage assembly). Be sure to use a level (you can find tons of "Level" apps in your smart phone's app store) to make sure you have a level X-Axis rod alignment. You need to make sure the rods holding your extruder assembly are perfectly level to get the most out of your machine.