Most servos have 90 degrees of travel.
You may be able to expand the range from your handset / receiver, but need this to be available in the settings of your radio gear. - Some has this.
The servo also has to support doing this. Not all do, and very few manufacturers tell you if this is a feature.
Your simplest answer is to search for a '180 degree servo'.
Also remember the linkage can not go 'over' a centre-point, and back down. - You can't arrange for the linkage to move from 10 o-clock to 2 o-clock, if the servo is below the regulator.
Some loco suppliers have a different regulator valve for manual and radio control setups.
This compensates for the reduced travel of the servo.
PhilP.