What do you mean ?
Do you want to use a firmware upgrade for an SLC5/04 CPU on an SLC5/05 CPU ? Not possible.
Or do you want to download a program for an SLC5/04 CPU on an SLC5/05 CPU ? Not possible, but modifying the CPU type in the RSLogix project from an SLC5/04 to an SLC5/05 is fairly easy.
Then there is the problem with the lesser memory on the SLC5/05, which may or may not be a problem.
You can check the memory usage in the CPU properties in the RSLogix project.
If that checks out OK, then indeed you can download the program.
Remember to set the channel 1 parameters before downloading because these will have been reset upon changing from a DH+ CPU to an Ethernet CPU.