How to target javascript from another frame?

[admin]

I have a 2 framed page. In the bottom frame there are some buttons that I want to be able to call the javascript in the 'main' frame and change some of the variables within it.

Any ideas how I target the 'main' frame?

This is the original script;
<input type="button" value=http://www.webdeveloper.com/forum/archive/index.php/" Increase Speed " onClick="slideShowSpeed-=500;if(slideShowSpeed<100){slideShowSpeed=100}" name="button">


This is what I tried but it didn't work;
<input type="button" value=http://www.webdeveloper.com/forum/archive/index.php/" Increase Speed "
onClick="'parent.parent.frames[\'main\']', slideShowSpeed-=500;if(slideShowSpeed<100){slideShowSpeed=100}" name="button">

Thanks for your help.