As Paul suggested, this is not simple if the figure numbers and/or letters are fields (and they should be either seq or ref fields) but as you wrote the examples showing just text here is a possible solution that doesn't go for the bonus points.
Code:
With ActiveDocument.Content.Find
.ClearFormatting
.Replacement.ClearFormatting
.Replacement.Font.AllCaps = True
.Text = "FIG[.sS]{1,2} [1-9]{1,}[a-z]"
.Replacement.Text = ""
.Forward = True
.Wrap = wdFindContinue
.Format = True
.MatchCase = False
.MatchWholeWord = False
.MatchKashida = False
.MatchDiacritics = False
.MatchAlefHamza = False
.MatchControl = False
.MatchAllWordForms = False
.MatchSoundsLike = False
.MatchWildcards = True
.Execute Replace:=wdReplaceAll
End With