You can name your device by editing /etc/hostname with your desired name of the device.

After a reboot the system is named.

The name can be displayed with the command: /bin/hostname

The name can be sent to a DHCP server by editing: /etc/network/interfaces

The /etc/network/interfaces contains configuration details for each network device.  To send the name to the DHCP server, add a -x option to the DHCP configuration as follows:

udhcpc_opts -t 10 -b -x hostname:$(/bin/hostname)

This part of the configuration line is the option to set the hostname:

-x hostname:$(/bin/hostname)