At the train stations and in the downtown there are some Money-exchange offices where they say no-commission but the truth is different: Usually they count their rates about 20% lower than elsewhere, which is understandably too much.
If you want to avoid such situation, just use an ATM instead, otherwise you can change just a small amount... only what is definitely required but not more! There are plenty of ATMs and money exchange offices all around the town! Please always check the rates on the Internet ( we recommend: www.xe.com/ucc ), the usual rates should not be more than 2-3% lower than the mid-rates!