Hi Nomoto,
Here is how you can change the UART port in U-Boot, kernel and user-space.
U-Boot: Build U-Boot with the following configuration:
make am335x_evm_uart2
Kernel: Change the "console" environment variable in the U-Boot bootargs:
console=ttyO2,115200n8
User space: Change this line in /etc/inittab:
S:2345:respawn:/sbin/getty 115200 ttyO2
Best regards,
Miroslav