Nvidia has done a pretty good job of keeping things up to date when it comes to its discontinued Shield Tablet. Since its release, the firm has updated it to Android 6.0, Android 7.0, and while it did confirm it wouldn't be updating the tablets to Android 8.0, it has provided smaller support updates. Now, the firm is upgrading the software to version 5.3, bringing necessary security features.
Perhaps the most important part of the new update is that it offers fixes for Wi-Fi vulnerabilities like KRACK and Broadpwn. The update is also accompanied by an Android Security Patch that will make it current as of November 5, 2017. It will also provide overall system stability improvements, along with security optimizations. Finally, the update also has a fix for people experiencing connectivity issues with Zagg Bluetooth keyboards.
The update should arrive on your product automatically, but if not, you can always hit the update menu in the settings.