how to restore to default, the desktop themes in windows 7 64 bit

HI, i changed the theme, the dark with yellow letters found in the windows 7 and customize some items without knowing that it would affect.
But anyhow, the background changes to unwanted dark colour and the entire browsing becomes difficult afterwards.
Hence, i tried others as well , but i do not like it.
what i thought is just increasing the size of font, but it changes the other thing as well.
how to restore the theme to its default
Is there any tutorial here or please give me a fix , on how to restore everthing back to the original default themes

Hi, brink, i could delete the theme in MY theme.
But what i want is , just restore the defaults to all the themes

i could not locate easily , as the selected letters are in dark blue and the letters are in yellow colour.
please give the exact item no in the tutorial to proceed.
Hope that you are in good health and spirit

Please tell the option in your tutorial link. Still not able to restore. Please give option

HI, still i could not find the exact option.
i already deleted picture in my theme by right clicking and deleting it.
i enclose a screen shot, and would be glad to have your fix
i did select high contrast, theme and changed something, there are so many items in the top pane in the enclosed picture. i selected desktop theme. i do not know, what was there in default.
the green colour , i mistakenly selected .

Hi, yesterday itself i replied.
ok, what i want is default to those high dark themes which i have customized .
i could just click and get windows 7 basic themes or other aeros theme as you have mentioned.
but my issue is with regard to changes i mede in the high dark themes
there are so many items of which i failed to notice the default menu exactly to

the green colour is one another thing.
how to restore their default is the query