Your speedo isnt programmable. To recalibrate it you replace the driven gear on the VSS.
Here is what the manual says for a 1998 F150........
Remove the original driven gear.
Ts = Number of teeth on replacement driven gear.
To = Number of teeth on original driven gear.
Va = Actual vehicle speed.
Vi = Indicated vehicle speed.
VSS = Vehicle Speed Sensor.
NOTE: Design accuracy is: -3/+8 km/h at 50 and 100 km/h (-2/+5 mph at 30 and 60 mph).
NOTE: Use one of the following formulas.
With Va, Vi, and To known, calculate new number of driven rear teeth.
Ts = (Vi x To)/Va
Ts = (To x new tire revolutions per mile)/(old tire revolutions per mile)
Round to whole number, dropping fractions less than 0.6, and rounding up if fraction is 0.6 or higher.
You can take it in or you can try it yourself. The VSS is held into the back of the transmission with 1 bolt. Remove the VSS and the gear is right there on it. You can count the teeth on it and then figure out what you need. Are you changing the speedo because of new gears or tires? I usually try to figure out the percent difference between the new tires and old tires or new and old gears and then go from there..... i.e. if the new tires have a 10% bigger circumference you would have to slow down the speedo by 10% which would mean you need a 10% larger driven gear......if it had a 20 tooth you would go to a 22 tooth.
I hope this helps.