In order to improve the circuit you have to first know what it is about it you want to improve. In what way could it perform better? What are the shortcomings in its performance? Once you know that you can consider what you can to to get the enhanced performance.
As for the PIC in the circuit what does it do? If you want to replace it with a different processor work out what it is doing and replicate that on your preferred processor. You don't need to know anything much about the PIC family, you just(!) need to know what it is doing in this case.