The key thing to remember is that all of the weight is at the bottom, so much like the Weeble, they're meant to wobble and not fall down. The description from here is almost certainly what your teacher is doing.
Basically, you tip the base at a 45 degree angle so that the edge of the bottom is on the floor, and roll the bag to where you want it.
That said, it's not quite as easy as that, depending on how much you weigh. If you're not strong enough to just tip it, what you need to do is grab as high up on the bag as you can, and then let your weight pull it back. One method I've seen used to good effect for people who don't have a lot of body weight is to step onto the base with one foot, grab the top of the bag, and then step backwards and to the floor, letting your extended arm and body weight pull the bag down as you use the other hand to keep it from falling. One you get it to that 45 degree angle, the weight of the bag is on the edge, which means you can roll it wherever you need it without too much trouble.
If you can't manage to tip it, you're going to want to push low, like you where doing a tackle drill. Once you get the bag moving, try to keep moving because you're dealing with the classic physics problem of static friction (what keeps the bag from moving from a standstill) generally being a bit higher than dynamic friction (the resistance to moving once you get something started).