how to change time step

i have data as monthly values and for 10 years and a total of 120 values for 120 months. and i need output also for each month and a total of 120 output values

[KSSV]

What? You have 10*12 i.e. years*months data which would be 120*n ....you can extract each month using data(1,:) right?

[Jan]

The question is not clear yet. You need output of what?