Sitebuilder freezing up for only 1 of my domains.

One of my domains has gotten fairly large and now when I try and add new images it freezes the builder I need to go into my computer resources and manually end the program. It is only for the 1 domain. Others all work fine. I tried moving parts into new folders etc but just left me with pages cannot be found so moved everything back. I need to add new inventory and not sure how to at this point.  http://www.emstshirts.com