File handling capabilities vary between the Files related list and Attachments related list in Lightning Experience and Salesforce Classic:
In Lightning Experience
Note: The Edit and Delete options within the downward facing triangle icon, on the View All Files page, are greyed out by design. Edit and Delete operations can be performed on the Preview page for the respective file as stated in the bullets above.
In Salesforce Classic
See also
Differences Between Files, Salesforce CRM Content, Salesforce Knowledge, Documents, and Attachments
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