Do you have control over the site or someone who works on it for you?
The absolute first thing you need to do is get gzip compression working for your html, css and javascript. It will speed things up quite a bit and if you pay for bandwidth it will save you money. If your hosting provider (or server if you are running it directly) has mod_deflate installed it should just be a matter of adding something like this to your .htaccess:
It’s trivial to implement and there are no risks associated with it.
There are two other changes that will have a HUGE impact but they are a little more involved:
1 - You need to merge your css files together into as few as possible (one preferred) and combine your javascript files together as much as possible (and reference the css before the javascript). That change alone should shave at least 8 seconds off of the start render and load times.
2 - You need to add expires headers to your static content so the browser will cache the files (all of the yellow highlighted requests in the repeat view can be completely eliminated). This is a little trickier because you need to make sure to change the file names any time you do an update but the win is well worth it
Don’t do anything else until you have at least addressed these 3 things and then you can take another look. The next biggest win will be in combining a lot of the page graphics into an image sprite which will eliminate a whole bunch of the individual requests for images.
Ultimately you should be able to get the page load time reduced by ~75% with just a little bit of work.
For #2, if you don’t want to worry about the downsides of having to change the filename per edit, you can always decrease the expiration time to something like 1 week or even 4-5 days. I’ve seen people get scared of adding these headers due to the possible increase in maintenance complexity, but even a shorter expiration time helps considerably (especially considering most users will view more than one page request in a single session).