Installing ubuntu on Apalis imx6 2G ixora

I am using Apalis iMX6 Quad 2G computer on module with Toradex Open embedded operating system. For my use case, i need to install ubuntu 16.04 operating system on my Apalis iMX6 Quad 2G so that this SDK will support.
To install that i have followed the steps given in this link

I have downloaded the Apalis iMX6 Linux LXDE image from their website and also downloaded the ubuntu 16 for iMX6 from this link. After that, i just copied everything from the ubuntu image to rootfs of Apalis IMX6 image. Then i have connected my apalis module serial port to the host. when i turned on the module and hit a key to stop from auto booting, it didn’t work. I don’t see any u boot prompt in minicom window.

What did i missed here? how can i enter into the u-boot prompt and after entering into the u boot how can i flash the OS?

Thanks in advance.

I would recommend using the Toradex Easy Installer and get your Ubuntu rootfs integrated as per the following.