Reformat USB stick with a CD ISO9660 FS

[Bevin Watson]

A couple of days ago the nice people from MBF handed out 512 Mb USB
sticks at the train station.  It has a small ISO9660 (CD) partition
which directs Windows users to their web site.  The rest (500 Mb or so)
is left as an empty vfat partition.
I did the right thing and went to the web site and read it in detail.
Now I want to give the USB to my child.  He is too young to take out
insurance so I want to remove CD partition to stop annoying pop-ups.
It says the CD file system is read-only (obviously) and won't let me
delete the files from it.  It seems the simplest thing is to just
reformat the whole device.  However, I'm getting a little out of my
league thinking about partitions versus the whole device.  fdisk etc.
seem to be partition-based.  Should I just "dd" all over it?
nb: The USB stick shows up as /dev/scd1 (ISO 9660) and /dev/sdd1 (vfat)