Are you looking to scale your design or just looking to upgrade to a 16-Bit PIC24 MCU? Microchip also has some great examples on their site linked at the bottom of the page that can help you find a good PIC24 for the part you are looking to upgrade. Here is an example of one of their path examples.
Microchip has also created a series of documentation to aid in your research.Below are a couple of great documents for you to check out if you are considering the migration.
PIC18F-to-PIC24F-Migration-and-Performance-Enhancement-Guide-DS00002991A.pdf (321.6 KB)
Mapping Peripheral Capabilities
Mapping Peripheral Capabilities from 8bit to 16bit PIC MCUs 30010196A.pdf (1.1 MB)
Migration Considerations Video
For more information and specific examples check out the Migration Page from Microchip.