Thank you very much. I was able to make what I wanted. Thanks for the reference
For future viewers, here's what I did.
If you will notice, in each dialogue UI, in my case Runic (Unity UI), it has an animator component. I was able to create a new animation clip, putted it in the controller and then call it in a specific dialogue via sequence using AnimatorPlay(). In the animator controller, I created a state: Fullscreen. The Fullscreen state has a default speed value of 1.
For example:
Conversation (NPC > PC)
*Hi > Hello > How are you > I'm fine thank you.
So what I want to do is make the dialogue UI's size into fullscreen in the "Hello" dialogue. So what I will do is call the animation state with the animation I created which will make the UI fullscreen in that dialogue's sequence.
AnimatorPlay(Fullscreen, Dialogue Panel). This will make the dialogue's size fullscreen like the middle picture in my first post.
Then after that, in the "How are you" dialogue, I want to revert it in the original size like the third picture in my first post, so what I will do is in the sequence of the "How are you" dialogue, I will write
AnimatorPlay(Start, Dialogue Panel).
Note that the "Start" state is already defined in the animator controller. Meaning it is already built when I checked the controller
Tha's all

And thank you again Tony.