Yikes, don't do what you're suggesting in your comment. You'll probably end up with multiple instances of Excel (check Task Manager and see how many there are after executing your code).
Firstly, add a reference to the Excel object library (Project->References & choose Microsoft Excel Object Library). Now you can declare your objects as bona-fide Excel types and use early binding rather than declaring them as "Object" and using late binding. This isn't strictly necessary, but apart from anything else it means you get Intellisense when editing your code.
You're doing the right thing right up until you do .OleFormat.Edit. (I would personally use .OleFormat.Activate but since I've never tried using .Edit I couldn't say that it makes a difference).
Having done .Activate (or, presumably, .Edit), you can then access the OleFormat.Object member. Since the embedded Object is an Excel chart, the "Object" will be the Excel Workbook, so you can do this:
Dim oOleFormat as OleFormat
Set oOleFormat = ...
oOleFormat.Activate
Dim oWorkbook As Excel.Workbook
Set oWorkbook = oOleFormat.Object
' Do stuff with the workbook
oWorkbook.Charts(1).ChartArea.Font.Bold = True
Note that you do NOT need to close Excel, and indeed you cannot - Word "owns" the instance used for an edit-in-place, and will decide when to close it. This is actually something of a problem, since there's no obvious way to force the embedded object to be de-activated, so the chart would stay open after you execute the code above.
There is a hack-y way to get the chart to close, though. If you add tell Word to activate it as something else, it'll de-activate it first. So, if you tell it to activate it as something non-sensical, you'll achieve the right result because it'll de-activate it and then fail to re-activate it. So, add the following line:
oOleFormat.ActivateAs "This.Class.Does.Not.Exist"
Note that this will raise an error, so you'll need to temporarily disable error handling using On Error Resume Next. For that reason, I normally create a Deactivate method, to avoid disrupting the error handling in my main method. As in:
Private Sub DeactivateOleObject(ByRef oOleFormat as OleFormat)
On Error Resume Next
oOleFormat.ActivateAs "This.Class.Does.Not.Exist"
End Sub
Hope this helps.
Gary