Take the Autobahn A5 to the Heidelberger Kreuz, and from there the Autobahn A656 into Heidelberg. At the end of the Autobahn, turn left, then immediately right, and follow the main road to pass under the bridge. Then turn immediately right so as to get onto the bridge and over the river. After the river, use the first possibility to turn left.
Take an Intercity Express (ICE), Intercity (IC) or Eurocity (EC) train to Heidelberg Main Station. From there, take bus Nr. 32 in the direction of Neuenheimer Feld (or alternatively the Straßenbahn Nr. 24, in the direction of Handschuhsheim), and get out at the "Jahnstraße" stop. The Institute is just a minute's walk away.
From Frankfurt Airport you can get to Heidelberg using the Lufthansa Airport Shuttle Bus or by train. Heidelberg is also easy to reach from the airports in Karlsruhe, Mannheim and Stuttgart.