Hi glenbar, if it is a smooth sided pot slip a narrow, blade like object, long enough to reach the bottom but not absolutely necessary and work round the pot in a sawing motion until you get to where you started..If the pot is too large or heavy to lay on its side go around enough to loosen the soil ball from the pot side , if you can tilt it, do so and slip your fingers down the side and ease the rootball out.Don't worry unduly if you break some of the roots as most plants respond with renewed vigour to a bit of root pruning. If it is a fancy-shaped pot you will need to use a similar knifelike object but a bit bendier.