When you start a dialog to open or save a document, LibreOffice initially displays your work directory. To change this directory:
Choose - LibreOffice - Paths.
Click My Documents and click the Edit button, or double-click on My Documents.
In the Select Path dialog, choose the work directory you want and click OK.
You also use this procedure to change the directory displayed by LibreOffice when you want to insert a graphic. Choose - LibreOffice - Paths - Images, then follow step 3.