A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Unfortunately that is not an option in Mac PowerPoint. There is no Link Manager dialog because the program doesn't support Linking. You'll need to delete the existing Excel object & create a new object from the preferred file. If the Link was created on a PC it may be better to have the updating done on a Windows box.
Excuse me for making an assumption but I get the impression that you may be relatively new to Office for Mac. If that's accurate you need to know that Object Linking & Embedding [OLE] doesn't work quite the same as it does in its Windows counterpart... Especially PowerPoint.
In a nutshell it doesn't support Links to anything other than images. When you copy & paste even a single cell the entire Workbook file is embedded in the presentation. There is no option to link to the Excel file. The embedded workbook can be opened & modified in Excel by double-clicking the object but the original source workbook will not be updated by any of the changes that are made. Likewise, any changes made in the original source will not be reflected in the presentation.