How can I call the constructor of a Class after it called once?
You can't. Once constructed, an object remains constructed until you delete it.

You could either use dynamic allocation and new and delete to create and destroy objects at will, or you could create multiple objects with different settings and use different objects at different times.

Another option would be to modify the library to create a new function that accepts and assigns new server settings. All the constructor does is store the settings in variables - there's no reason why you couldn't just change those variables.