Hi, I bought my kitchenaid artisan coffee machine on ebay. I can't get the steaming of the milk right. It froths too much so can't make just a latte or flat white. It looks to me that the nozzle holes are too big.

There is an art to working a foamer ... hence the "artisan" in the coffee-maker's name. There are several aspects to a good foam:

1. If you have been using regular milk to make your foam, try half-and-half ... the thicker consistency will give you a different result.
2. If you have been jamming the foamer head all the way to the bottom of the milk while you are foaming it, try submerging less of the foamer ... this will cause the steam to have a slightly different effect on the milk. If you have been submerging it only about half way (or not at all) try different depths. If one consistent depth is not right, try swirling it around while you foam the milk.
3. Try a different amount of steam (if your steam release valve is adjustable). Pushing a lot of pressure into the milk will give you a different result than barely turning it on.
4. Are you using a cold container or a warm one to hold the milk you are steaming? If you are still not getting the results you are looking for by playing with the other aspects of your foaming process ... try a different container (it sounds silly, but it can really help).
Before you go out and spend a bunch of money on different replacement parts for your machine, spend a while playing with these aspects of your foaming process. If none of these ideas help, then you should consider replacing pieces. Foaming milk is not as easy as it sounds ... it took me a few months of (once daily) use to really get my technique down so I could make a reliably decent foam. Don't give up! and good luck!