Here are the FAQ pages:
http://www.futaba-rc.com/faq/index.html
You'll find that the FAQs for the 12FG, 14MZ, and 18MZ will likely do the job. Other than how you scroll to the different entry fields, they are all basically the same, as far as programming goes.
To set exponential, select EXP1 or EXP2. Dial the number to a negative value. -50% is a good place to start for both values.
To have the changes be effective in only one condition, you must select the condition, go to the second page of the AFR and change "GROUP" to "SINGL", and then set the EXP values you want for that condition.