RESOLUTION
There is no possibility to change the SSL certificate for Expand through the control panel in current versions. However, you can set up the SSL certificate manually as it was shown in the example.If Expand is installed with Plesk together, then you have to add the SSL options below into the /usr/local/psa/admin/conf/httpsd.expand.include configuration file.
SSLVerifyClient none
SSLCertificateFile /usr/local/expand/etc/expand.crt.pem
Where /usr/local/expand/etc/expand.crt.pem is the file with the SSL certificate you got from CA (Certification Authorities).
In standalone Expand version you should look into
/usr/local/expand/frontend/conf/httpd_vhost.conf for SSLCertificateFile
and SSLCertificateKeyFile directives to find the certificate location.
Certificate and private key are stored in /usr/local/expand/frontend/conf/httpsd.pem file .
NOTE: Since version 2.2 standalone Expand uses it's own web server (Lighttpd) with /etc/sw-cp-server/applications.d/01_expand.conf configuration file. And path to the certificate is /usr/local/expand/frontend/conf/httpsd.pem.
If you wish to setup CA certificate, use 'ssl.ca-file' configuration directive. Upload your CA file to the server and add the following line to the /etc/sw-cp-server/applications.d/01_expand.conf file
ssl.ca-file = "/path/to/CA.crt"
Then restart Expand:
# /etc/init.d/sw-cp-server restart