To delete your TARDIS, you break the sign above the door of the TARDIS Police Box.
Note: As of version
2.7 the TARDIS Chameleon Circuit is no longer required to be set to a Police Box preset. Any sign on your TARDIS can be broken to delete it.
You will be asked to confirm the TARDIS deletion with a command. Type:
To confirm the deletion.
WARNING: You will lose any items you have stored in your TARDIS; all rooms, and any saved time travel destinations (unless stored within the TARDIS Disk Storage Container) will be removed.