To change the system console, change the "linux_boot_args_console" variable in "boot/uEnv.txt".
linux_boot_args_console=console=ttyPS0,115200
linux_boot_args_console=console=ttyPS1,115200
linux_boot_args_console=console=tty1
For Ultra96/Ultra96-V2, the system console can be changed in the boot menu when u-boot starts. In this case, add the following to the end of "boot/uEnv.txt".
########################################################################
# Boot Menu Example
########################################################################
bootmenu_0=Boot Default=boot
bootmenu_1=Boot ttyPS0=env set linux_boot_args_console console=ttyPS0,115200 && boot
bootdelay=5