You can move an item to another category, thereby recategorizing it:
Move the item at point to another category (todo-move-item).
This prompts for a category to move the item to, displays that category,
prompts for the priority of the moved item in the category moved to and
inserts the item accordingly. Minibuffer completion of the name of the
category moved to works as with the navigation command j, and as
with that command, passing a prefix argument prompts for a file and
moves the item to a category in that file; and if the category name you
enter is new, then you are asked whether to add the category to the
file, and if you affirm, the item is moved to the new category.
You can delete an item, thereby permanently (and, as far as Todo mode is concerned, irrevocably) removing it from the todo file:
Delete the todo item at point (todo-delete-item; the binding is
mnemonic for “kill”, since d is used for marking items as done
(see Done Items); but note that k does not put the item into
the kill ring). This command requires confirmation that you want to
delete the item, since you cannot undo the deletion in Todo mode. (You
could use F e to recover the item, but be aware that this would
put the file in an inconsistent state, which you can recover from, but
not without a risk; cf. the cautionary note in Reordering Categories.)
Note: Todo commands that require user confirmation, such as k, use a modified form of
y-or-n-p, which by default only accepts y or Y, but not SPC, as an affirmative answer. This is to diminish the risk of unintentionally executing the command, which is especially important with commands that do deletion, since there is no Todo command to undo a deletion. If you want to be able to use SPC for confirmation, enable the optiontodo-y-with-space.