The Dialogue UI included is an example/template which works a specific way (eg pushing dialogue up to show choices and typewriting the text). You are totally free to change the UI in any way you like though, since it is completely decoupled from the actual dialogue (graph) functionality. I would suggest to for example make a copy of the GUI as a starting base and modify it to fit your project needs by altering the code and/or of course the UI elements themselves. All the relevant code can be found in DialogueUGUI.cs file (the component attached on the @DialogueUGUI prefab gameobject). The part for example where the dialogue is pushed up, can be found on line #244 in that script.
Please let me know if that helps or if I can assist you in any other way.