Galaxy Express 2 CM 13 (CyanogenMod 13, SM-G3815) Marshmallow ROM is an unofficial build brought to you by developer kotzir. As this is an unofficial build you may not expect periodic releases but everything is working on this ROM except the NFC, because of lack of source code.
Before proceeding further you may consider backup your all data. You are the only person doing changes to your phone and I cannot be held responsible for the mistakes done by you. Neither the developer nor we will be held responsible for any disaster that happens to your device.
Recommended files for Galaxy Express 2 CM 13 (CyanogenMod 13, SM-G3815) Marshmallow ROM installation:
Installing Galaxy Express 2 CM 13 (CyanogenMod 13, SM-G3815) Marshmallow ROM:
Copy the ROM and Gapps zip file to your SD card or internal memory(By using a USB cable or via adb push command).
Reboot into recovery by pressing key combination or type the following command if you are on a PC:
$ adb reboot recovery
Wipe Data / Factory Reset.
Format cache, Format /system partition.
This step may delete all your data. Consider backup your all data out of your phone.
Select the Install Zip from SDcard option.
Select the CM 13 Marshmallow ROM zip file for the Galaxy Express 2 where you have kept in the SD card and do the same for GApps also. After finishing flashing just reboot your phone and enjoy CM 13 Marshmallow ROM on your Galaxy Express 2 (SM-G3815).
There is a development thread in xda forum created by kotzir (Developer of this ROM). If you have any concerns on this ROM then you can visit the forum page and speak out your problem.