Apple TV model a1218 how to securely erase?

I want to sell a A1218 model (first generation ) but i want to make sure nobody can retrieve any home video files that I have historically copied on to it.

I was thinking of dismantling the device and securely erasing the hard drive in another mac then re-install the apple o/s but i appreciate that will involve a lot of work.

I am unsure that if by doing a standard reset,that it would actually securely erase the files or,like most o/s's do,just erase the locations of the files,

Has anyone any suggestions please?

(or what i may do is just remove the drive and sell it as is to someone who technically can re-fit a larger drive and re-install )