SO you installed your SSL certificate and when testing on https://cryptoreport.geotrust.com/checker/ you have got this image:

Indeed SSLv3 is not secure and you should disable it. How? If you use Nginx simply go to the website block (config file in the nginx/sites-available) and add this line:

  ssl_protocols TLSv1.2 TLSv1.1 TLSv1;  

It would look like this (some data was wiped off):

Before you restart the Nginx please do the test:

nginx -t

If everything is fine you would get a message:

nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

Now restart the Nginx:

service nginx restart

Run the SSL test again and the problem should be solved. Enjoy