Updating firmware stored in a rewritable non-volatile memory as a plurality of firmware code images having position dependent code. A plurality of update code images are made available that have position dependent code specifying positions of a rewritable non-volatile memory, such that each update code image is suitable for replacing a different stored code image. A computer processor determines which stored code image is to be updated; and selects the one of the plurality of update code images that has position dependent code suitable for replacing the code image to be updated.