If you removed the bolts and the rim is stuck to the axle you can use penetrant as mentioned and tap the back of the rim with a dead blow hammer. Before remounting apply a little never sieze where the metals meet each other.
To break the tire bead I lay them on the garage floor, place a 2x6 or similar on the edge of the rim and drive my tractor up the board.
Breaks the bead every time.