The program won't let me save the changes I made in the preferences

Eh, hello. I’m new with this program and I don’t know what the hell I have to do to resolve my. . .little problem. It’s kind of simple, really.
Well, the thing is that when I open the Preferences, the window is too big and doesn’t let me making it more little so I can’t push the OK button. It’s that. And I don’t know what I can do. It’s exasperating. I’ve trying different things to make it more little but it doesn’t make it any better. I can’t save the things.
Thank you in advance, if you can help me.