Do you mean the red and yellow buttons in the top left of the window? I'm not sure if it's possible to change the size of those, but a few things you could consider:
1) Lower the resolution of your display (making everything appear larger)
2) Use the Zooming feature in the Universal Access section of System Preferences, which will make everything on screen bigger (but you'll have to pan around to see the edges)
3) Use keyboard shortcuts to close/minimize windows instead of the mouse:
Apple key+m to minimize
Apple key+w to close
Maybe there is a way to enlarge those buttons that I don't know about, though.