Castling in GLChess

This may not be the right place for this but I can't figure out where else to post this.

I'm playing GLChess on Ubuntu but cannot figure out how to castle. I've seen the computer do it but I can't seem to get it to work for me. I also cannot find this in the help.

Again, if this is the wrong place could somebody point me to where I should be looking?

Thank you.