Changing the screen size

I recently replaced my ancient computer with a new and better one. I have re-installed AOEII almost successfully, however the game only takes up part of the screen. The screen size selected is 1024 x 768 and I cannot click on 1280 x 1024 which I assume would fill the monitor screen. I did not have this problem on the old computer. I am now running Windows 10 rather than Windows 8. What should I Do?