The Screen menu in Super Smash Bros. Brawl gives an in-game means of changing the widescreen settings of the Wii console to match the television being used. It is accessed via the Options menu, from the main menu, and by default inherits the setting enabled in the main Wii console options.
The two options are:
A circle appears in the background on this menu, to help the player to see which screen size is more suited to their TV.
Note that changing the screen ratio does not change the Wii's output resolution, which remains at 640×480 (even on the default PAL setting of 576i, 50Hz), only the way the picture is rendered within that resolution. As a result, snapshots captured on a widescreen-set console will appear to be "squashed" horizontally if decrypted and viewed on a PC unless resized.