What is the syntax to find and replace a value?

Sht.Cells.Replace What:=<old value>, Replacement:=<new value>, LookAt:=xlPart, MatchCase:=False
'example - replaces all instances of person's name
'Old first/last name are in A1, B2 (respectively) in Sheet "Names"
Dim Sht As Worksheet
For Each Sht In Worksheets
    Sht.Cells.Replace What:=Sheets("MasterNames").Cells(1, 1).Value, Replacement:=txtNameFirst.Value, LookAt:=xlPart, MatchCase:=False
    Sht.Cells.Replace What:=Sheets("MasterNames").Cells(1, 2).Value, Replacement:=txtNameLast.Value, LookAt:=xlPart, MatchCase:=False