There is possibly an easier way, but from what I understand about R/C you would need to alter the connections from the servos to the reciever. On a 2 channel set simply swap them over. On a set with more channels, remove one (mark it), check to see what doesn't operate, remove another, check, until you have identified which lead goes to which servo, then Re-position. What you must remember is that the servos will be trimmed for what they were originally intende for and if you don't understand how to re-trim you could have problems. Some sets will only let you trim 2 out of for channels. Something else to think about is some channels may be reversed, there is usually a swich on the transmitter.
Like I say there is possibly a much easier way, I only know this from doing what I do, your set up may be totally different?
Mal