row = 6
NameOld = Cells(4, 1)
Do
NameNew = Cells(row, 1)
Cells(row, 2).Replace What:=NameOld, _
Replacement:=NameNew, LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False, _
SearchFormat:=False, ReplaceFormat:=False
row = row + 1
Loop Until Cells(row, 2) = ""

Hth,
Merjet