How to Delete Files from your iPhone SE

Deleting iPhone files while hooked to Laptop
* in iTunes, on left panel under Observatory's iPhone, click on music
* You'll now see every song and mp3 on the iPhone.
* click on an mp3 description, right-click and delete from library. Now, that sounds like it only deletes from the library and not the iphone but...
* it'll ask for confirmation to delete this file from the iPhone, and then it's gone.

Doing it from the iPhone

* Desktop, tap Settings > General > Storage & iCloud Usage.
Under Storage, tap Manage Storage.
* tap iTunes Music icon
* Find the audiobook you want to delete, then swipe left on it.
* Tap red Delete.