Go to: Windows > Developer Tools > Widget Reflector
Change the “Application Scale” setting.
WARNING
Some of the drop down menus are rather long and if they don’t have enough screen space they kind of glitch out. For instance, the “Windows” menu is pretty long and if you set the number too high, it can be impossible to find and select “Developer Tools” again to change it back. I recommend changing it from 1 to 1.1 or 1.2 to start with. I finally settled on 1.25 myself, but I first tried 2. Big mistake.