To upload themes or plugins on Multisite, please use the "network" page of your network. This means not your network's main "blog" but the network admin page. Please go to Empire Builder ==> Manage Themes or Empire Builder ==> Manage Plugins
You will reach the right page :-)
Also, if you are getting a "1500 kb" error, check the solution here.
Article ID: 42
Category: WP Empire Builder