cannot delete twenty fourteen theme

I am unable to delete the twenty fourteen theme on a wordpress website.

The person who owns it hasnt used or maintained it in a few months, and i had to gain access again by changing user password in mysql databse (got to that via cpanel-luckily for them i happened to still have one of the emails they sent me many months ago with their cpanel username and password).

I need to delete the theme because
1.the theme will not update (cannot remove theme error appears when update fails)
2. The main wordpress CMS will not update either (still on version 3.8.3)

Whenever i try to delete the theme files using ftp…i get 550 permission denied error.

If i try to delete directly through cpanel file manager…the files delete then reappear again less than a minute later.

This theme is not the active theme!

Any help would be appreaciated