Admin features not available

I recently became the webmaster for a website that was setup by someone else which uses WordPress as a multiuser site using sub-domains. There are currently several sites already set up, however, I am not able to add additional sites as there is no link to do so even when I am logged in as a Super Admin. Likewise, there is no plugin section in the admin panel. I tried to update the site to the latest version of WP to see if that would resolve any of the issues, but again, even as Super Admin it says I don’t have rights to do the upgrade.

Unfortunately because of the relationship between the site owner and the previous designer I am unable to get help there. I have worked with other multisite installations and have never encountered issues like this.

Does anyone have an idea of what might be going on or where I could get assistance to resolve these issues?