Terminal -> Preferences -> General -> Shell opens with:

Update as needed, the following are available by default.

/bin/bash
/bin/sh
/bin/zsh
/bin/ksh
/bin/tcsh

These can also be set from the command line using the following commands.

chsh -s /bin/bash
chsh -s /bin/sh
chsh -s /bin/zsh
chsh -s /bin/ksh
chsh -s /bin/tcsh