The reason a lower unit seems "stuck" and won't come off is because there's a part, and only one, that runs from the top of an outboard motor to the bottom: the shift rod. Beginning just beneath the power head of the motor, where it's connected to the shift shaft, it runs down the exhaust tunnel to the gearcase in the lower unit. If it isn't released, you cannot remove the lower unit, even if it is unbolted from the exhaust tunnel. So take a minute and release the shift rod if you want to remove the lower unit.
Reach behind the motor cover and turn the latch on the back to unlock the cover. Lift the back of the motor cover upward and release the hooks under the front edge of the cover. Lift the cover off the motor.
Reach under the front edge of the motor and release the spring clip that holds the shift rod to the shift shaft.
Pull down on the lower unit. Take care to pull the lower unit straight down to avoid bending the shift rod or the drive shaft