What OS are you running? I would think it would have some function to allow you move windows that are larger then your display so you can move the windows so part of the window frame is on screen so you can then re-size the window.
For example I just move my Chrome browser window sot the top of the window is behind the task bar. I now can not move it necause I can mot position the mouse int the window header bar. However I can position the mouse over the running Chrome icon in the task bar. Windows will show a preview of the running Chrome window or windows. If I right click on a preview window Window's will open a right click menu I can click on the move item and them move the off screen window on to the display using the arrow keys or the mouse.
Which of the little colored OSX buttons at the upper-left is it that turns "full screen" applications into "windowed" ones? I'm a PC user, and it's been a long time since I've been on a Mac. I know it seems obvious, but have you tried pressing whichever button that is?
Another possibility might be to try disabling and re-enabling the Application Frame (in the Window menu).
Noel, you are a star! I really don't know how both myself and my wife missed that obvious option, but we did!! Thank you very much, Richard
Thank you very much for getting back to me, turned out to be a very simple click away! (see below) Macs are fine when used by experts!! I much appreciate your help, thank you, Richard