Mac Kext are like drivers for the Windows platform. You need them to get your hardware device working. In Mac the device drivers are mostly from Apple, therefore unless a third party is willing to give support, unsupport hardware is very difficult to co-exist with the mac os. This is a way to update kext manually from the terminal.
To update a kext:
cd /path/to/new/kext (put your downloaded kext path here)
cp -R KextName.kext /System/Library/Extensions
next you need to fix permissions so the kext can be executed by OS user (root/system)
chmod -R 755 KextName.kext
chown -R 0:0 KextName.kext (this will set the ownership on files to system user (root))
rm /System/Library/Extensions.mkext (this will reset all kext caching done by OSX)
Another way with GUI is to use the Kext Utility, by downloading this and using it, it will fix kext automatically. If you want to install kext, you can drag the kext onto the program directly, the program will install and update the Extensions.mkext file.