From the airport - if it is not a taxi (trip around PLN 80, c. 20 euros) - take the shuttle train (tickets on board or from vending machine in arrival terminal) to the main train/bus station.
From there, we suggest you take a tram no. 19 (direction: Borek Falecki). This is an underground line and the stop is located just under the platform of the airport train. Get off at fifth stop called "Miodowa", turn right into Miodowa street and proceed to number 28. You can buy tickets from machines inside a tram, and just remember to validate them.
Walking from the train/bus station takes approximately 15 minutes. You need to get to the underground passage situated in front of the ancient main train station building. Leaving to the left, take ulica Westerplatte and get to the big Post Office building, then take a left into ulica Starowislna (not to confuse with ulica Wielopole), cross ulica Dietla and straight along ulica Starowislna get to ulica Miodowa. Now you only need to take a right and proceed to number 28.
Taxi stands are located above train station platforms, in front of the bus station building, or in front of the shopping centre. Expect to pay no more then around PLN 20 (c. 5 euros).