FTP Server Failure

I downloaded the underConstruction plugin and I got logged out of admin. This plugin displays an under construction page for members not logged into the site.

I looked up this problem and someone suggested using FTP to log in and remove the plugin. However, when I tried logging in, authentication failed and I couldn’t connect to the server.

I am entering my username and password correctly. Why is this happening? Please help, I cannot edit my site or have access because of this plugin.