SharePoint - Unable to delete a locked or checked out document
Site Administrators can take ownership of the file(s) and then check them back in.
SharePoint - Steps to delete a locked or checked out document that is checked out by someone else.
1. Launch site/page where documents are located.
2. Select the Library Tab and click on Library Settings.
3. In Library Settings, select the "Manage files which have no checked in version" option.
4. Select the specific document you want to take ownership of.
5. Click on "Take Ownership of Selection" link at the top of the list.
6. Once you have ownership, you can now check in the document and manage it appropriately (delete, update, etc.)