Typically there is a lock/cam ring that is turned to release the disposer. If the cam ring is corroded in place, you may gave to cut or break it to get the disposer out. Loosening the screws above will only give you a big, big headache; now the the disposer and drain flange will be loose and locked together - the drain flange has to go up to be removed and the disposer has to go down. With it all loose it will be harder to cut or break the two sections apart.

Are you trying to loosen the flange at the top of the disposer like shown at minute 2:20 of this video https://www.youtube.com/watch?v=_u9ulIo5Xfc ? Do you have a long screwdriver or metal rod you can insert in one of the holes to get more leverage?

This guy (https://www.youtube.com/watch?v=tpGe7YiQLV0) explains how he bent the three flange "tabs" which allowed him to remove the disposer.

Yes, that's what I've been trying to do and it won't budge. I may try to bend the tabs if I can get to all three.