Adjust grid system on single product page

Hi there,

I've searched a lot in the forum, but I didn't find the solution. On my single product page, the product image takes almost 50% of the total width - now I'd like to make the image "column" smaller and the column including Product name, price, etc. bigger. Adapting the image width is easy to implement, but as I reduce the image width, nothing happens to the columns. How can I easily adapt these in desktop view?
User & PW for my site are: nextend

Thanks for help.
Frank