If it's a DIG-220 control panel, you can safely go to any size cell without any other modifications. The SC36 and RC5 cells are the same. Also, there are new part numbers for all the cells. RC5=SC36=RC35/22; SC48=RC42; SC60=RC52.
Once replaced, go into the installer menu and adjust the CELL TYPE to match the same model cell that you replace it with. Dont forget to replace the cell cord at the same time.