Originally published at: https://www.cyberciti.biz/faq/change-my-default-shell-in-linux-using-chsh/
How do I change my default shell in Linux?
By the command usermod, for example. Have a look to the manual.
Anyway, to set csh:
sudo usermod -s /bin/csh <username>
Usermod can be used to manage many other parameters of the account, like expiration time for password, adding groups, etc.