Find a metal rod that easily fits through the bearing centre (1/2" should do it). Now, with the bearing elevated, tap around it, never hitting in the same place twice (you want the bearing to come out square, not on an angle). Keep doing this until the bearing falls out. Then turn the wheel over & repeat the process.
To fit the new bearings, use a small block of wood to knock the bearings in, checking after every hit or two to make sure it's going in square. You can also use a large socket the same size as the outer ring of the bearing. Keep going until you hear the bearing "bottom out". Trust me, you'll know, the sound changes