Go to:
Client and Editor\resources\gui\layouts\game
Then open one of the below in notepad++ and edit the file for the textbox size and such. Each one of the below 1, 2, 3 or 4 represents the amount of text buttons for the response from the player:
EventDialogWindow_1Response.json
EventDialogWindow_2Response.json
EventDialogWindow_3Response.json
EventDialogWindow_4Response.json
They each have components called:
EventDialogArea
The EventDialogArea(s) have parameters called bounds in the format:
<Bounds>X, Y, W, H</Bounds>.
The Y value is how far from the top of the window the dialog area is at. The H value is the height of the area.
You should be able to lower the Y value to make the chat area move upward, and increase the H to make it taller.
Here is more help if needed: