To change the coil in your Mini V4 vape tank, first turn it upside down so that the mouthpiece is pointing towards the floor.
Then, unscrew the rough-textured section from the tank, and set the part which holds the liquid to one side.
You'll see the coil sticking up from this rough-textured section, so simply unscrew it, and screw the new coil in its place.
Then, fill your tank, screw everything back together, and leave the tank to sit right-way-up for around 10-15 minutes, so that the coil gets properly saturated in your preferred e-liquid.
Then, attach the tank to your battery and you're all ready to go!