How do you unscrew the hood of a 29 gallon all-glass aquarium? I really need help!?

I bought a “29 gallon all-glass aquarium” from Walmart a year ago. I want to switch lighting fixtures but I have no idea how to get the hood open to unscrew the bulb! If you turn the hood over you see the glass and the bulb, but there are no screws or anything. I really would like to change the fixture. Thanks.