A server with a double-firmware storage space and a firmware update method therefor are provided. The server includes a baseboard management controller (BMC) with a control module and an update module, a selection circuit, a first storage circuit, and a second storage circuit. The control module executes a first firmware program from the first storage circuit. The update module stores a second firmware program in the second storage circuit according to a firmware update instruction when the control module executes the first firmware program. The BMC resets after the second firmware program is stored in the second storage circuit. After the BMC is reset, the control module obtains the second firmware program from the second storage circuit and executes the second firmware program.