Question Using UI for dialog in VR

Hello I am trying to make a dialog system in a VR game. As of right now I am trying to us UI to display what the NPC is saying with text and a button that i want to use to progress the conversation. as of right now i have a canvas set up with text and a button. I have looked everywhere but I cant find a way to change the text to the next line of the conversation when I click the button.