Deleting nandroid backup made in CWM?

OK, so I originally had CWM recovery on my tablet and I created a nandroid backup through there to my internal tablet memory which used up like 5.5gb of my 11.95gb of usable space. Shortly after making the backup I decided to flash twrp recovery instead...

Now, how can I delete the CWM backup without having to reflash CWM recovery??