You can upgrade easily, but downgrading requires special software to do, which I believe to be proprietary to Xerox. (Tech call needed)
Xerox only ever has one firmware per device posted, which is the latest General Release.
There is also always a link that can be obtained easily enough to the latest spar (Call and ask for it)
Any firmware in between might as well not exist , it is near impossible to get if you don't have it already as Xerox does not want people using "known bad" configurations. If you need a specific version, you need to archive it yourself.
Assuming you are printing via an LPR port and not RAW, the following should resolve the issue you are seeing.
Machine Status > Tools > System Settings > Print Service Settings > Allocate Memory > Recieveing Buffer - LPD > Spool to HDD