Most of them just lift up, there usually there is a latch on the right that moves to unlock the machine from the bottom case.
Lift up, then look under the machine for the grub nuts. There should be 2, don't lose them, very small. They unscrew.
I did have one machine that had a screw that lifted up to loosen the machine from the case. If you have a featherweigh machine you have to unscrew the bottom screw under the machine.