Read the specs/datasheet of your controller and your development 
toolchain. Point out what's important for your project. Then go to 
microchip.com, view the required controller line and set the filters for 
the requirements you just found out. After that a couple controllers 
remain. Read carefully through the specs and through your code to see 
how much effort remains to port the code to the new controller. Test the 
result to verify before producing a batch.

That's how you are going to do it.
However, I'm happy to assist.

According to my honorary policy this initial advice is free of charge. 
Further service will be charged $0.05/character including spaces or 
$100/hour whichever is higher.

Sincerely yours