FOTA update to Android M is expected later and you will receive regular updates, no worries. Don't update on Android M now as it is full of bugs.
You can download the firmware from the link and save in internal memory. Phone will detect the update. Also do a factory reset post updating. Backup data in memory card before factory reset
Just Place the Downloaded Zip file on the internal storage of your device , and restart the device, it should show the update prompt. It is recommended that you factory reset your device before and after the upgrade..