First, unscrew and remove the base hardware and pull out the coil.
Then invert the tank and using the special key provided, unlock the top hardware by placing it in the slot of the screw holding the top hardware (see diagram).
Next, remove the glass tube. Replace the glass tube and follow the steps in reverse, (it is easier to place the screw onto the key first to locate it into the top hardware), secure the screw, insert the coil and replace the base hardware.
Remember, before using a coil for the first time to let it stand for 5 minutes after filling with e-liquid to saturate the coil and avoid dry hit and damage to the coil.