The auxiliary channel on RC seems to be stuck on channel 8 which emits PWM of 1500 and when I try to switch flight modes via the switches on the RC the channel 8 PWM does not change staying on 1500. The other channels are fine (ch.5, ch.6, ch.7) and respond to the switches. What I want to know is how to switch the auxiliary channel from 8 to 5 (on my spectrum dx7s if that helps) as the flight modes respond to channel 5. I have seen the link where it tells you what to do (copter.ardupilot.com/wiki/channe … -8-options) however the decription does not apply tomy situation as the software is out of date (I’m currently using MP 1.3.34) and it decribes what to do in reference to a copter (I have an Aero-M). Any suggestions would be most helpful. Thanks. 
Not sure I follow your post but surely being a DX7s, you don’t have a channel 8??
FLTMODE_CH can be set to the channel you want to use to change flight mode’s (5, 6 or 7 on a DX7s).
This is the page you need for Plane flight mode changing.
plane.ardupilot.com/wiki/common- … iguration/
Its different to copter.
Thanks, Grant.