I wonder if my Third party externals folders in App > C74 and things in the clipping or extra folders will be deleted if I update to the last version?

third-party-externals

it should necessarily stay the same, as the update replaces the main program and not the gubbins in-between.

at least that is what i know when using say, other peoples externals and keep them in the max externals/msp externals etc folders. they stay there once i do update.

but if you are still not sure, i would suggest copying your third party externals folder onto the desktop, then moving it back once the update is done...