Change icon in slider

[Sander Bloem]

    Im wondering how i can change the "icon" cg titel in a slider..


What i have is a slider for controling a light fixture the button is indicated with the following symbols: <   > but i need to change this to: -    +.
below you'll find the slider that we use for dimming the lights.
   

but i need to change this into the following with the slider function.
   

is there a way i can do this?

Thanks alot!