This is the safest method for regular users and does not require a computer. the update.zip file specific to your model. Copy the file to the root folder of your phone’s SD card.
While a custom ROM like LineageOS could theoretically breathe new life into an old ZTE Blade V30 Vita, there are significant risks: Firmware ZTE Blade V30 Vita
Use the volume keys to select "wipe data/factory reset" and confirm with the Power button (this will erase user data). This is the safest method for regular users