4.2.1 jb

If I have 4.2.1 already jb and want to upgrade to 4.2.2
Is there a way I can upgrade without having to rejailbreak?

No.   Anytime you upgrade to a new firmware release you lose all current settings and need to re-jailbreak.    You therefore need to make sure there is a jailbreak available for the firmware vesion you intend to move to.