Thank you so much for sharing knowledge about "How to Fresh Install" and "How to Upgrade"

yes! download stock rom first and then you can follow given steps.

For Fresh Install warning:
1) Please do not upgrade the phone with non-official firmware
2) Upgrading international version phone with the mainland China Simple Chinese version firmware may lead to compatibility issues
3) Before upgrading, check that the battery has at least 20% capacity
4) Selecting "Clear data" will delete all personal data ( such as Notes, Email, and Contacts); whereas the internal storage for Music and Camera photos ...etc. will remain intact.
5) Already opened system permission (ROOT), the user must select "Clear Data" to clear phone data for firmware upgrade, Otherwise, it may cause abnormal system or application error ;

6) After upgrading the firmware, if system reboot or application force close, please try to reset your phone or re-upgrading (Settings-> phone->Storage->Factory reset to reset the phone)

Upgrade procedure:
1) Copy firmware "update.zip" onto the phone, open the "Documents" and click the firmware "update.zip" to upgrade firmware
2) System upgrading, please do not shut down the phone
3) The system will automatically reboot after upgraded
4) After boot up, please check “Settings->About” to verify the correct firmware version is installed