- Download the latest u-boot revision from GitHub:

$ git clone https://github.com/UDOOboard/uboot-imx


- Move inside the folder uboot-imx, and enter in the A62 branch:

$ cd uboot-imx
$ git checkout imx_v2014.04_3.14.28_1.0.0_ga_a62


- Use the script compile.sh with the -c option to choise the configuration of the board you need and compile:

$ ./compile.sh -c 


- The compiled U-Boot binary (u-boot.imx) will now be available in the current folder, you can flash it in the microSD with "dd" command:
(NOTE: Be sure you’ re using the correct device filename; 
use of the wrong device identifier could result in the loss of all data on the Hard Drive of the host PC used.)

$ sudo dd if=u-boot.imx of=/dev/sdX [ or /dev/mmcblkX ] bs=512 seek=2