Search and get the latest twrp.3.3.1-12 by brigudav.you can get it here to.
https://t.me/PyxisVelaChannel/287
Put new rom on memory card
In twrp, FORMAT DATA (were you type YES to confirm)
Reboot to recovery(IMPORTANT)
factory reset
Flash rom
Wipe cache and dalvik
Reboot to system (it'll take a...