Given the age and low specs (likely 512MB RAM, 4GB storage), no firmware update will make it run modern apps well.
Only download firmware from reputable sites or the official Lava Support Center to avoid malware. lava iris 42 firmware
If your is experiencing software glitches, such as being stuck on the boot logo, suffering from frequent app crashes, or becoming unresponsive, installing the original stock firmware (Flash File) is often the most effective solution. Given the age and low specs (likely 512MB