Despite the new software build, however, the Android version will remain the same even after the update. The updated build number for these devices will be LMY48M, except the carrier version of Nexus 6 for T-Mobile, which will have the build number LYZ28K.
This update will be the first of monthly updates that were recently promised by Google after the Stagefright vulnerability was identified; following the criticism, the search giant committed to providing regular updates for its devices.
Since the updates are just security patches and no new feature will be added, their size is only about 20MB. However, for the Nexus 6, it may be slightly bigger, at 30MB. In general, these updates will be quick to download and install on your devices.
If you have not yet been notified of the security updates, chances are that you will soon receive a notification; the upgrades are still being rolled out. Once you do get it, all you will have to do is to command the device to install them, and the rest of the process will be the usual, automatic one.
So sit tight and wait for it. Also, be ready for such updates n the near future; Google plans on releasing them regularly!