1. Login to Plesk Control panel
2. Select the domain name in which you need to install ssl certificate
3. Click Website and Domains
4. Click Secure your sites
5. Click Add SSL Certificate
6. Upload the certificate files
7. Private key - Browse your private key
8. Certificate - Browser your 'domainname.crt' file
9. CA-Certificate- Browser your 'domainname.ca-bundle' file
10. Note: If you haven't get the CA-bundle file, please contact our ssl support.
11. Click Send files.
12. make sure that you have selected the SSL certificate Option
13. To check this, Click Website and Domains >> hosting settings >> SSL.
14. Click Home.
15. Click Tools and Settings.
16. Click Service Management.
17. If your server is running Linux, stop and start the Apache process. If your server is running Windows, stop and start the IIS service.

Note: If you cannot able to find the options specified on the above steps, then please contact your server support where you hosted your website.