Summarize:

. Older Nexus devices and other older devices using Android 4.4.2 or earlier did not get the Google Now Launcher update, and are locked at five home screens. The only way to get rid of the extra home screens is to install a different launcher.   You can install the Google Now Launcher from the Google Play Store.  Nova is another popular launcher that allows you to delete extra home screens, along with a host of other features.
Install a new launcher