I currently own a 2020 Ford F250 with the latest version of sync 3. Is it possible to upgrade it to nav without changing out the APIM?
There is a hardware hack that requires you disassemble the APIM and replace one of the cards, but it is risky and not supported here. It would also affect the warranty on the APIM unit, Just FYI. I would advise against it unless you are proficient in programming software and firmware is the Sync environment.
New take-out 2019 APIM’s for North America vehicles are available. (2020 not so much yet.) You could review the classified sections of websites and even EBay. (Be careful to make sure you verify the part numbers vs model year, 2019 is K, and 2020 is L for the first digit in the part number). Since you have a F250, I recommend you visit the F150Forum and read the Sync and FORScan threads. There is a wealth of information on that site related to what you would like to do.
No. Your non-nav APIM does not have the required storage.