Also, create a space identical to the size of the pot you are transplanting from in the new pot. Do this by adding soil to the new pot to get the desired height (place the plant and current pot in the new pot and + or - soil to get the height). Then remove the pot, water, and repeat (soil will settle a little when you first water). Then place the pot back inside and sidefill till you get the height you want. Water throughly and you will probably have to repeat. Make sure that soil is wet. Then remove the pot from your soil....and presto....nifty little space identical to the current pot (you can add root stimulator to the hole). Remove the plant from its current pot and as quickly as you can without damaging the root mass put it into the hole.... should fit nice!

Remember do not press the soil down, let the water settle the soil. If you press the soil down the roots have a harder time getting into the new soil.

it has been the easiest way for me.....

IMO this should be done inbetween waterings, if the soil is to dry then you have soil falling from the root mass, if it is to wet then the weight of the root mass breaks it apart when removing the plant out of the pot.