Apple - Change Terminal.app's Default Shell to BASH

Open System Preferences, select user and right click on its name. "Advanced options..." will appear. Change shell there. If you're die hard Apple user, you probably will have to enable right click first. Depending on your computer model, it can be done under Trackpad or Mouse Preferences.

By using chsh from Terminal. It changes default shell for user. Alternatively you may setup Terminal to use /bin/bash -l ... this will cause BASH to behave as login shell, i.e. it will read .bash_profile.