How do I install the plugin into my website?

Hello! I created an account under my name to install a plug-in into the website. Unforunately, I did not create an account with the actual wordpress account that I need to install the plug-in into. With that said, I am having difficulty installing the Membership plug-in into the website. What is the best way of going about this? I have a weblink that I use to access the admin page for my wordpress.