Change Wakfu installation folder

here's my problem : When I launch Wakfu from Steam, it installs some files on my first HD (in the Appdata\Local folder) but there is no more space left in it (all my steam games (even Wakfu) are installed on my second HD) so it won't install the game completely. My question is : how can I change the default folder of the in-game installation ?

Thanks in advance.