can't delete from my shared folder

In the Finder, do a Get Info on that folder and look near the bottom for Rights & Privileges, change them if need be to you, then check the files in there the same way, also check if any are Locked.

Since another user had created the content, you will have to
supersede their privileges in order to remove the file; if you
have authorization to do so, and the file contains nothing the
business may see as proprietary to their interests.

You may be able to change the read-write access & remove it.

Good luck & happy computing! 🙂

There may be some backdoor way into doing that; but I have not really been
looking into that long, since I don't share my files using the shared folder &
my own computers with multiple user accounts are not that big an issue.

Apparently some other users have had issue with trying to change user
permissions in a system and have rights to previous and now gone user
files migrate or be moved more easily to the present set of active ones.

{A way probably exists in the Terminal or other 'super user' mode; that is
not activated by default & seldom is ever used except to serious things.
Then, it would deactivated once the one issue was cleared. A business
owned computer may be a different matter than a personally owned one
in regard to accessing the deeper levels of the OS to change privileges.}

Some of this is discussed here: Quick and easy folder sharing in 10.5
http://www.macworld.com/article/133207/2009/11/105foldersharing.html

Note the section of the article with the sentence starting:
"...If you delete a user who still has rights to a shared folder..."

When the user, whose file you want to delete, is no longer there and/or
if their account has been deactivated, sometimes it may become neces-
sary to re-activate or recreate the account to regain privileges to do it.
And this has been a rub in come instances, where the user's files were
not removed before the user was removed from the computer.

Perhaps someone has more insight into this matter and has a simpler
resolution. There is a path through terminal or super user access; or
maybe there is a bootup method that ignores users, such as SafeBoot
where a file could be found then, trashed, then the computer restarted
normally? {I've not tried that. - And it seems too simple to work...}

Good luck & happy computing! 🙂