Jaybird2005 was pretty accurate in that ceramic knives are pretty tough guys. Most are made out of zirconium oxide (8.2/10 on Mohs scale where Nanodiamond is the highest at >10/10). Hence, one of the few ways to sharpen them is by using a diamond stone/wheel. However, unless you are very proficient at sharpening, I would suggest having the knife professionally done simply because of how expensive it would be if you mess it up. One alternative might be to purchase a "cheap" ceramic knife (paring knives tend to be cheap enough) to use as a tester until you feel comfortable. I'm very surprised that the knives are dull after just 6 months. Do you have a warranty?
I don't even know how many times I sharpened my crappy knives before I was comfortable enough to purchase and sharpen my current set. 20+ years of sharpening knives on a daily basis and I still wouldn't mess around with sharpening a ceramic knife, just my $.019
http://youtu.be/Oqn7vcByIgo