Need to change pin for Redbearlab nrf51822 board for spi communication

I am using redbearlab nrf51822 board in arduino ide , default pin configuration compatible for arduino is as follows:

SS- 10 // P0.14 for nRF51422 board PCA10028
SCK- 16 //P0.25
MISO- 17 ///P0.22
MOSI - 18//P0.30

I get the data by this pin configuration but I want to change this pin configuration to :

SS- 10 //P0.14
SCK- 15//P0.20
MISO-17//P0.22
MOSI-4//P0.21

How do I change my default pin configuration to the one I need ??