The first thing we have to do is make sure we have the package installed dosfstools.
$ sudo aptitude install dosfstools
Once installed, we will check where our flash memory is located. We can use the command:
$ sudo fdisk -l
Which will return something like this:
The line that interests us is the one that says:
/dev/sdc1 * 62 7983863 3991901 b W95 FAT32
Once we know which device to format is, we use the command:
sudo mkfs.vfat -F 32 -n Mi_Memoria /dev/sdc1
With option -F32 we tell you that it will be formatted as fat32, and with the option -n We put a label or name to the device.
Edito: I forgot to say that to execute this operation, the device has to be unmounted.