Recently installed avast on a laptop with 1366x768 display (windows 7 64bit), and avast GUI windows were too big, goes offscreen, some options not visible, for example uninstall option. Some windows can’t be closed since the title bar with close icon offscreen. Make it smaller.
Works for me, probably related to your graphics settings (DPI).
I agree with vastix. The whole GUI window should be capable of being maneuvered, if not resized, by a pointing device, e.g. the left mouse button being held down while the pointer is over anywhere on the area within the perimeter of the GUI.