Usually you don't pay for FTP access, but you do need software, like Filezilla, and the login details. Which consist of the ftp address (ftp.yourdomain.com), your username and password.
Your hosting company should have sent this information when you created your account.
You can read more about Filezilla here: https://codex.wordpress.org/Using_FileZilla
Once you get access, delete the problem plugin.
If you're not confident doing this, contact your host, they should help you fix it.