NOP is only a pupplet and so has the same release number as the parent Puppy (301). The various R's will therefore not trigger the puppy upgrade. The only way to do this is to replace the pup_301.sfs file in your frugal install. Also if going from R3 to R6 it is best to also replace the initrd.gz file.
This may not work or only partially work and may need a couple of reboots to stabilise the updated system even if it does.