Although DISKPART is a way to do it, be very careful when going that route . Diskpart wipes any choosen drive without asking further questions, so be always sure you chose the right one. At the least the tools mentioned above are the safer choice .
The active one gets an asterisk when listed again, there is also the detail command. After you have chosen the disk with select disk <no.>, just type detail disk. Just give your USB pen drive an unique name to identify it (and verify the capacity as well).