To reconfigure no-ip setting:
sudo dpkg-reconfigure noip2
It will ask you the same questions as when you installed it: your login (email adress), password, updating interval (refresh the record of your ip adress), hosts (also known as subdomains. you can insert multiple hosts, comma or space separated.), network device name (if you have broadband connection (configured by pppoeconf), enter the adress of that connection, usually ppp0), NAT (network adress translation).
After this it should say something similar to this:
Auto configuration for Linux client of no-ip.com.
4 hosts are registered to this account.
Host myhost.myftp.org selected.
New configuration file '/var/lib/noip2/noip2.conf' created.
* Starting No-IP.com dynamic address update noip2 [ OK ]