editing a site html

the site [login to view URL] was made for me by another programmer who did it really badly. I would like the following errors completed. 1. the site loads up in a funny manner and sometimes gets stuck before fully loading 2. all the images are very big and dont load up fast.. so i asked the coder to implement a thumbnail module in the cms.. to upload a low res thumbnail which links to the high res image.. but this is not working it is purely still showing the original image not the thumbnail. 3 . there are a few bugs I want ironed out simple project shouldnt take long