How do you change your monitor to widescreen?

I have a HP w1707 monitor and now there is black on both sides of the image whenever I watch a video on Youtube or whenever my screensaver pops up. I was told at one place that it had to be switched back to widescreen, like it used to be. (When I 1st got it, the image fit the screen perfectly-on Youtube it looked a tad strange, but not a huge annoyance. And this coming from a person who actually doesn't even like most widescreen).How do you change your monitor to widescreen?
try the F-12 button

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