How to make an installer

I am trying to make a disk that will copy & replace some files

however it wont replace/delete startup

everytime it trys it gives me the reason

Install:1: Access Denied

here is my code:

fs.copy("disk/startup", "rom")
fs.copy("disk/password", "rom")
print("Installation complete!")
sleep(0.25)
print("Rebooting")
os.reboot()

You can't copy it to rom, rom is read only memory. What you probably want to do is copying it to the main directory. Like this:

fs.copy("disk/startup", "startup")
fs.copy("disk/password", "password")
print("Installation complete!")
sleep(0.25)
print("Rebooting")
os.reboot()