The "W300 series" is a family, not a single device. Using the wrong firmware will break your modem. You must check the .
Once you have obtained the verified file from ZTE, follow these steps to update: ZTE WXV10 W300 - Multiple Vulnerabilities - Exploit-DB download firmware modem zte zxv10 w300 series verified
Known legitimate firmware versions identified in official documentation and vulnerability databases include: W300V2.1.0f_ER7_PE_O57 W300V1.0.0a_ZRD_LK How to Update Safely ZXV10 W300 Wireless Access Point Quick Installation Manual Verified Download: ZTE ZXV10 W300 Series Modem Firmware