Installing Plugins

Hi, I’ve been using WP that I dl’ed and installed using an external hosting plan and have no problems. Now I want a second wp site and have signed up for the wp premium plan, the problem is I cannot seem to install plugins with this plan? On externally installed site there is a button for plugins where I can search and install new plugins. With the wp hosted site the plugins button leads to link asking if you want to upgrade to install ecommerce and info about the hosting plan. Does that mean that I cannot install plugins with this plan?
Thanks in advance.