table adjustment

hi,

i have two rows split into two columns (header rows). below, I have several more rows split into 4 or 5 columns (body rows).

I now need to adjust the sizes of the body row columns without affecting the header rows. However, when I manually go to push and tug at the columns, it is shifting everything, including my header rows. How do I get it to understand? I am selecting the body rows and not the headers, but it still picks up on those.

thanks!