Log into your Raspberry Pi (by ssh for example) or open a terminal window if you are working directly on Pi. In the first step we have to install ddclient, a DynDNS software, on the Pi. For this purpose, the following two commands are necessary.
sudo apt-get update
sudo apt-get install ddclient
Note: During installation an installation wizard opens and wants to know some things from you. Here you can safely enter what you want, because we have to adjust the configuration file manually either way, because the wizard does not support the Namecheap.com interface.