The pangu jailbreak tool you are using supports iOS 9.2.1,so personally I don't think you need to update the iPhone to iOS 9.3.3 1st.
Some research on google got me the information that the Chinese jailbreak team,pangu are NOT going to release a untethered version of ios9.3.3 jailbreak,so you are stuck with a semi-untethered jailbreak with ios9.3.3.
Remember to full backup your data in iTunes!
1)Make a full backup of iphone in iTunes.
2)Restore iPhone to factory settings.
3)Activate new iPhone.
4)Jailbreak iPhone.
5)Restore from backup.