I know that if you're using a gamepad, you can click through different sizes for the currently selected window (or the selected HUD element while rearranging them) by clicking the right analog stick. No idea what the keyboard shortcut is, but I'd try selecting a window and pressing plus or minus, for starters.

This is a really handy function to know, especially if you're like me and don't like too many HUD things cluttering up the screen. Works on the PS4 and I would presume the PS3, as well. The sole exceptions are the chat and the map, which can be resized with the mouse by click and dragging the corner.