My PC diusplay has corrupted, not what was, and cannot get it back fully to what it was (dialog boxes much too small; rest of display ok). Minded to replace driver. When do so, understand must delete existing (which is the same). But thought occurs - if I do so, will I still see what is on the screen, prior to installing new driver, i.e. for the period between deleting the one and replacing it with the other, I will not have a display driver, so why then should I still be able to see anything at all - no driver - or is this a daft question?

you will still be able to see your screen, your computer will use the standard vga graphics driver, it will look big on screen but you will be able to see to install the new one :)