Hi Linda,
Welcome to Box Community and glad to help!
Note that your ability to make changes in a folder or file (i.e. upload, edit, delete and whatnot) varies according to your collaboration access, especilly if it's a collborated folder or file.
Seems that you don't have access enough to be able to delete a file. At this rate, kindly contact the owner.
Find out more about collaboration permissions by visiting this helpful article.
Thanks for posting!