How to clear the file field?

in my form i have a file type field
lets say the user choose a file then he change his mind and don’t want to post any file. how can we remove the selected file so it will not be uploaded?

I think the best way would be to have a form reset button that resets the form. You could probably even have it reset just that field of is a large form.

Form reset is the way to go.
Due to security reasons, especially in older browsers it is not possible to alter the file input contents using javascript.

So the user must refill the whole form?
I think this is not great for user convenience but thats html i guess.