You can download Cyanogen Mod 13 for the Moto E first generation which beings Android Marshmallow to the smartphone
Thanks to folks at xda developers, Moto E users are able to finally enjoy what it feels like to have Android Marshmallow on their smartphones. Interestingly, Cyanogen Mod 13 for Moto E first generation is quite stable for daily use. Even the dual SIM functionality works like a charm. Of course, display, wireless LAN, SD card, GPS, Bluetooth and Camera works as well. Download CM12 for Moto E 2015 from here.
Installation instructions for Cyanogen Mod 13 for Moto E first generation
* Wipe data and cache. Make sure Moto E bootloader is unlocked.
* Flash the CM13zip. Downloadable from here. Of course you need to have Moto E custom recovery to flash it.
* boot into recovery mode.
* Install gapps if you want
That is it, you now have Android 6 marshmallow on your smartphone. Moto E is showing its age but till we have xda developers, we do not have anything to worry about.