clean usb stick with partitions

If you are running an Ubuntu system and have a related question, why do you post this in the area for "Launchpad" and not in the "Ubuntu" area?
I am going to move this question to the right area.

For manipulating partitions there is the program gparted (eventually you have to install it first).
Whatever there is on the USB stick, you should be able to get rid of it by deleting the partition(s).

Use caution not to select the wrong device (e.g. your system's hard disk).