PBP's default configuration for the 18F25K22 uses the Internal Oscillator for the Primary Oscillator.
So all you need to do is set the OSCCON register.

OSCCON = %01010000 ; 4Mhz
OSCCON = %01100000 ; 8Mhz
OSCCON = %01110000 ; 16Mhz

Or, if you enable the PLL with ...

OSCTUNE.6 = 1 ; Enable 4x PLL

Then ...

OSCCON = %01010000 ; 16Mhz
OSCCON = %01100000 ; 32Mhz
OSCCON = %01110000 ; 64Mhz

Make sure your DEFINE OSC matches.