BER to the centre is the S-Bahn (S9 or S45) or the FEX express, about 30 to 45 minutes.
One BVG ticket covers the U-Bahn, S-Bahn, trams and buses. The arena is near Warschauer Strasse and Ostbahnhof.
Plan your route to Uber Arena ahead of time, and leave early to beat the crowds.