Directions:

From Hamburg Airport:

Take the S-Bahn S1 to the main station (Hauptbahnhof) and change to the S21 in the direction of Dammtor.
From Dammtor station, it's just a 5 minute walk along the Rothenbaumchaussee.

From the Main Station (Hauptbahnhof) in Hamburg:

Take the S-Bahn S21 or S31 to Dammtor 
From there, a 5 minute walk along the Rothenbaumchaussee.