AR-300m upgrade uboot to newer verions

I have this router purchased Nov 2017, flashed the latest 2.263 NAND firmware via the GUI, I then flashed the LEDE 14.01.4 NOR firmware via UBOOT web update. Now I want to be able to boot the NOR image by using the switch.

What is the current procedure? What is the latest tested working uboot image? I have no UART adapter at the moment, is it possible to flash new uboot via a web gui?