In order to increase the nic content, just order some more juice of the same flavor with the next higher nic level and mix them together - example you have 12 mg nic and want it to be about 16, you can either order 24 mg nic and mix it with the 12, or just order 16 and mix it with the 12 to get a slightly higher level. You can order just the nic juice, but read the warnings first. Nic juice in higher levels is "poison" , mix at your own risk.