if the upper floor is still locked, maybe you have to click the door in the Main Room, to access its bathroom, there you will find the way to unlock the stairs.
I'm not sure what you mean by the main roon.... after breaking the first spell from ground floor to first floor there would be 2 doors. Is the door on the right is the one you mean? Because it is locked.
Edit: Oh nevermind I found it. Didn't see that door at all until now lol thank you
