The firmware is virtually the same as that on the t520 and t630. Press F9 during POST for a boot menu, F10 for setup, F12 for network boot, or ESC for a startup menu.
Both UEFI and legacy boot modes are supported, but I have not tested legacy mode.
The flash chip for the firmware is socketed (same type of socket as the t520/t630) and I have not tried updating it.