I'd like a Drupal Developer to fix an error on our site.

I believe we use Drupal 7.59 on our site, so it's pretty older. There is some error on our site that is prohibiting me from deleting a pdf file that is displayed/accessible on the site. I'm getting error messages whenever I try to delete it. The first screenshot shows what the file looks like on the front end. It looks like there are 2 separate error messages occurring. If you look at the 2nd screenshot… when I click the 2nd (bottom) “Remove” button, this error message pops up (403 error code). If I click the first (top) “Remove” button instead, then it seemingly works, but then when I click “Save” it takes me to the following page (3rd screenshot) with a 500 error code. When I then go back to that page, the file is still present. We had a developer look into the issue and they said: "when trying to save the form in the CMS, Drupal tries to find a function that appears to no longer be supported by the Drupal core file (referred to as deprecation)". Unfortunately they are unable to fix this issue cheaply. I need someone to either (1) fix this issue so the error messages stop coming up or (2) find a way to delete the file yourself - whichever is easier and quicker.