I want to speed up my website www.reisomdewereld.nl.

Hello,

I want to speed up my website http://www.reisomdewereld.nl. Because it's too slow. Now only the frontend, but if i work in de cms, it's also very slow at some moments.
I have allready done the most basic things, installed a caching plugin, smush it pro, upload not to big pictures, etc, etc and the website is hosting on VPS, But i am not a core developer and i hope you can help me with some more advantaged improvements.
You can look in the backend of my website cms and see what improvements there are to speed up my website. Are there possibilities that a core developer can do the changes/improvements for me?

Greetz, Marcel