Hello, there is an asterisk server running in my company, but its managed only by command prompt. I wanted to see if im able to install FreePBX in order to configure and manage the current server through web interface without having to reinstall with current Asterisk settings.

If so, how do i do it without losing anything? Thank you.

That will not work. If you do that you would be asking for trouble. FreePBX makes its own config files and it will over ride what you already have causing data loss. Even if you backup what you have now and were to move it over once FreePBX is done installing you would not be able to manage that stuff though the FreePBX web interface.