If you want to increase the header size of columns you go to the window where you want to change it, then you right click on the headers and this window will come up:
Then you go to ”Behavior appearance” and go to “Header lines”, here you can choose the size of the headers, if you want them to be bigger you choose “3” and if you want them to be smaller you choose “1”. Remember to click “Ok” when you are done.