To uninstall Tails from a USB stick, and use it for something else, you have to reset it.
The content of the USB stick is lost in the operation, but an attacker might still be able to tell that Tails was installed on that USB stick using data recovery techniques.
Using the Disks utility
You might overwrite any hard disk on the computer.
If at some point you are not sure about which device to choose, stop proceeding.
Make sure that the USB stick that you want to reset is unplugged.
Choose Applications ▸ Utilities ▸ Disks to start the Disks utility.
A list of all the storage devices on the computer appears in the left pane of the window.
Plug in the USB stick that you want to reset.
A new device appears in the list of storage devices. This new device corresponds to the USB stick that you plugged in. Click on it.
In the right pane of the window, verify that the device corresponds to the USB stick that you want to reset, its brand, its size, etc.
To reset the USB stick, click on the button in the title bar and choose Format Disk to erase all the existing partitions on the device.
In the Format Disk dialog:
If you want to overwrite all data on the device, choose Overwrite existing data with zeroes in the Erase menu.
Overwriting existing data does not erase all data on flash memories, such as USB sticks and SSDs (Solid-State Drives).
See the limitations of file deletion.
Choose Compatible with all systems and devices (MBR/DOS) in the Partitioning menu.
Click Format.
In the confirmation dialog, click Format to confirm.
To make sure that all the changes are written to the USB stick, click on the button in the title bar.
Resetting a Tails USB stick from itself
If Tails is your only Linux system, you can generally reset a Tails USB stick directly from that USB stick while running Tails.
When starting Tails, add the
toram
boot option in the Boot Loader.If Tails starts as usual, follow the instructions for resetting a USB stick using the Disks utility.
If the system fails to start, that means that the computer does not have enough memory for this operation mode. Try with another computer, or find another Linux system, such as another Tails USB stick, to do the reset from.