Dig around in the new pot, soil to break it up good, or in the bag or a bucket before adding to the new pot.
Water it so it settles a little.
Dig a hole at least 1" deeper than the plant seems to need and at least 2" larger diameter, to account for settling of soil later and caving of the side walls while setting the plant in.
Get plant out of old pot, stick your finger up into the bottom of its soil and pull sideways gently to expand the roots a little. Don't overdo it.
Place in new pot hole, sprinkle on more or scoot nearer the soil till it reaches a uniform flat layer.
Water in that and soil will settle a bit more. Top off soil again to reach a flat surface.