Indeed, if you had used the Caption Style, it would have been a simple matter of Ctrl-A, F9.
For what you now have, you'll need a macro like:
Code:
Sub Demo()
Application.ScreenUpdating = False
Dim i As Integer
With ActiveDocument.Range
With .Find
.ClearFormatting
.Replacement.ClearFormatting
.Text = "Figure:"
.Replacement.Text = ""
.Forward = True
.Wrap = wdFindStop
.Format = False
.MatchCase = False
.MatchWholeWord = False
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
.Execute
End With
Do While .Find.Found
i = i + 1
.Text = "Figure" & i & ":"
.Collapse wdCollapseEnd
.Find.Execute
Loop
End With
Application.ScreenUpdating = True
MsgBox i & " figures updated."
End Sub
FWIW, deleting the old numbers as you've done doesn't really help - the code to replace the old ones could have been almost the same.