A method and apparatus for upgrading software held in read-only storage are described comprising non-reprogrammable read-only memory (116) which stores a file manager program (120), program file A (122) and program file B (124) and a Flash.RTM. RAM (118) which stores file X (132). Under control of the file manager program (120), when an upgrade program file B+(126) is acquired, for example via the Internet, it is stored within Flash.RTM. RAM (118) and file X (132) is updated. When the software executes, file A (122) calls file B+(126) in preference to calling file B (124), in accordance with the contents of file X (132).