When tapping a hyperlink, a list of web-viewing capable apps will be presented – if you have not yet set a default. Tap on the app you wish to open the link with (in this case, Chrome) and then tap one of two buttons, labelled ‘Always’ and ‘Just once’.
The latter allows you to open a link in an app without having it set as the default choice, whereas the Always option will set the chosen app as the default viewer. If an app has been accidentally set as the default, go into the Apps section of the Settings app, then swipe rightwards to the All tab and scroll down to and tap on the app you wish to unset as the default browser. Now tap the button labelled ‘Clear defaults’ listed in the ‘Launch by default’ section.