Keep the soil in the container moist until planting time. Set the shrub, still in its container, into the hole to confirm the correct depth. Then lift it out and remove the container from the rootball.
If the shrub has begun to outgrow its container it may be potbound. Free as many matted and circular roots from the outside layer of the rootball as you can, spreading them outward so that they aim toward the sides of the hole when you set the shrub in it. Sometimes a screwdriver or similar tool is useful to pry them apart. If they are terribly matted, you may have to clip off some, or even take a sharp knife and slice down vertically through the roots into the soil ball at 2 or 3 places around its edge.