How to flash LEDE only to GL.iNet products

I’m not sure how to flash LEDE only to your routers. Any suggestions?

There is nothing special, at least regarding MT300A. Simplest is, to ssh into router,
cd /tmp
download the openwrt-/lede image to flash
sysupgrade (-n) image.bin

Or do it from the GUI, BUT do not keep the settings.