Yes, since you want to replace all sorts of "bk" at the end of the string, you can use UCase, like in the code below:
If UCase(Right(Cells(i, 1), 2)) = "BK" Then
Cells(i, 1) = Replace(Cells(i, 1), "bk", "", 1, -1, vbTextCompare)
End If
Note: adding the last parameter of vbTextCompare to the Replace function indicates that it's case-insensitive, and will remove all sorts of "bk".
Edit 1:
In case you have multiple occurrences of "bk" in a certain string, and you only want to remove the one at the end of the string, use the code below (thanks to @Ron Rosenfeld):
If UCase(Right(Cells(i, 1), 2)) = "BK" Then
Cells(i, 1) = Left(Cells(i, 1), Len(Cells(i, 1)) - 2)
End If