You may want to try the module positions I suggested in the other post. But if you do want to make the right column bigger for other modules.
You first need to increase the size of the site wrapper div, this is currently 980px wide, becaus it's a good width for people on laptops. You could decrease the width of the main column but that's slightly more involved and is already quite narrow.
On line 112 of template.css you'll find the wrapper ID
#wrapper {
width: 980px;
}
I'm going to make it easy and say we want to increase it by 100px. So make the width 1080px.
Then on line 170 is the right column css.
#farrightwrap {
width: 180px;
}
Make that 280px. Now it'll still look like its small because the repeating background images are still the same width. The images that need changing are
commtechcooling.co.uk/joomla/templates/t.../
images/left-mid.png
commtechcooling.co.uk/joomla/templates/t.../
images/left-top.png
commtechcooling.co.uk/joomla/templates/t...ages/
left-bottom.png
It looks like you've increased the top and bottom images but the because the middle one is applied as a background image the only way to control the width is by editing the image source. It'll look slightly better if you edit the image so they all have the width you want to change it to, in this demo case 280px.