Copy your web server certificate out of the email from WEBYSSL.com and into a text editor such as notepad and save as yourdomain.txt.
1. Click on the Domain link to view all domains. Click on the relevant Domain Name.
2. In the Services section, click the Certificates icon
3. In the section labeled Find the appropriate private key to the certificate click Browse to locate your yourdomain.txt file
4. Click Send File to upload your certificate. Plesk will restart automatically and will now have installed your certificate