The fields are content controls and they appear to be locked against deletion, which is a sensible thing to do. If you cannot enter multiple lines of text then they appear to be plain text controls. You can change them to rich text which will permit formatting and multiple lines.
You can change the property of each control you wish to aqccess to remove the lock which will allow you to modify or delete it. However I am not familiar with the Mac interface and initial enquiries suggest that there is no interface to access to properties in the Mac version.
All may not be lost as the Mac version can run macros and the following macro should unlock the two controls and either convert them to rich text format which will allow multiple lines or you can remove the apostrophe from the 'oCC.Delete line and the controls should be deleted. Much depends on what the Mac version will allow.
Code:
Sub Macro1()
Dim oCC As ContentControl
For Each oCC In ActiveDocument.ContentControls
Select Case oCC.TITLE
Case Is = "Title", "Subject"
oCC.LockContentControl = False
oCC.Type = wdContentControlRichText
'oCC.Delete
Case Else
End Select
Next oCC
Set oCC = Nothing
End Sub