NASA Press Release: 

Expedition 14 is readying the station for a reboost, the relocation of a Soyuz spacecraft and the arrival of its replacement crew.

On Thursday, a docked Progress 23 cargo craft will fire its engines to lift the station into a higher orbit. The reboost is necessary to put the station into the correct altitude for the upcoming docking of a Soyuz spacecraft carrying the Expedition 15 crew.  

Two weeks later Commander Michael Lopez-Alegria and Flight Engineers Mikhail Tyurin and Suni Williams will enter their Soyuz TMA-9 spacecraft to undock from the station and redock moments later to another port. The relocation allows Expedition 15 to dock to the station when it arrives on a Soyuz TMA-10 spacecraft.

The Expedition 15 crew launches from Russia on April 7 and will dock to the International Space Station on April 9. Expedition 14 will leave the station and return home in its Soyuz TMA-9 on April 20.