It's interesting that you used exactly the same phrasing as another poster, (different username), earlier:-
me and my groupmates
Will all that be possible in the Gui? If yes, give me some insights of how to make the code since we have a little knowledge in visual C. and If no, Do you have any suggestions to how can we make alternatives of the said functions of the GUI.
This is an Arduino (C++) forum. There's no point in asking questions about C# GUI coding. You need a C# forum, to ask about serial communications in C#.
And you can't "change some parts of the code of the arduino" using the C# GUI app, but you can send serial comms that determines which code is executed.
If not a specialised Visual C# forum, perhaps you should have posted in the "Interfacing w/ Software on the Computer" section of these forums, instead of "Project Guidance". Maybe you could ask a moderator to move the thread for you.
(And C# questions aren't really 100% suitable there either.)