By default, Aspire will run on port 50505.
You can change this port address by editing the file config/felix.properties. Find the property org.osgi.service.http.port and change it to the desired port.
Also, if you want to run more than one instance of Aspire on the same server, remember to update the property osgi.shell.telnet.port, which by default takes 6666. See Accessing OSGi for more details on what this port is for and how to remove it.