Sur le git de multibit il y a des instructions pour migrer

https://github.com/Multibit-Legacy/multibit

Next Steps for Multibit Users
Videos that demonstrate how to move your wallet to Electrum are available on YouTube.

Multibit HD: https://youtu.be/E-KcY6KUVnY
Multibit Classic: https://youtu.be/LaijbTcxsv8
Please note that the version of Electrum available for download today (version 2.8.3) doesn’t fully support the importing Multibit HD wallet words. The version shown in the Multibit HD video is the soon-to-be-released next version.