Pulled this off of this Prophecy link
3.1 What is ROM?
ROM stands for Read Only Memory, and usually comes on a computer chip. In this case, the ROM contains the operating system of the synth. It controls the computer and chips inside the Prophecy.
3.2 How do I know what ROM version I have?
Press and hold ENTER and EXIT during startup.
3.3 What is the difference between ROM versions?
(From earlier FAQ:) ROM #13 was in the first batch of keyboards, #16 is the most common one and the latest out (and regarded bugfree I think) is #20. See also question 3.4.
3.4 What is the current/latest ROM version?
Latest is ROM #20, or Prophecy 1.20.
(The following submitted by Nick Rothwell Tue, 26 May 98):
"According to a contact at Korg UK, ROM #18 is functionally identical to ROM #20; the latter contains some more debugging features for repair and servicing. My Prophecy (ROM #18) works fine in the situations reported to need #20..."
3.5 Where/How do I get an upgrade?
At your nearest music shop, it should be free.
The ROM is delivered on a chip, and either you or the dealer can install it. If you haven't done stuff like that let the dealer do it. Again, according to Korg the upgrade should be free of charge. However, some list members has paid for theirs.
Please note, most music dealers won't have the chip laying around, and has to order it. Phone and ask before bringing in your Prophecy, as it might be gone for some weeks.
3.6 Will there be more upgrades?
Probably not. Rom #20 is regarded bugfree by Korg. There will not be any new features, so no need for another upgrade.