Same advise as every reality TV show.
Check the official webpage for the show that is the one the network put up.
That is where you will find the casting information.
http://www.fox.com/hellskitchen/ They have a link for future casting for the show in the middle of the web page. Not sure when they will be casting again as the season that airs starting April 1st should already be complete. They do have a place to email right now. As the get ready to cast the next season you usually find more info (dates for casting calls, application forms, etc.)