I wanted to know If I can change server type for an ISPCONFIG already installed from nginx to apache? if yes how? Thanks.
It should not be impossible, but you might run into unforeseen complications. If this is a empty server, simply reinstall with the ISPConfig autoinstaller and pass the correct argument to install nginx instead of apache. If you want to try anyway, uninstall apache2 and all it's modules, then install nginx, change the configuration of the webserver in the panel, and run a forced ISPConfig update (and let it reconfigure services)
Like @Th0m mentioned, switching from Nginx to Apache or vice versa is possible, but it's not easy and requires good Linux admin skills as likely some things will break and need to be fixed in config files manually then. So, if you have the option to reinstall the system, then that is the better choice.
