Hi Rooftop!
If your planters are bursted it will be easier work. Just rip the old boxes off, cut away as much old root as you can- removing about 3 inches of the old soil/root mass and add new soil Then re-box with new wood. You can also do the same as above-then box in with a larger box with more new soil. I would suggest this on any plants that just haven't been happy in the size box they have. In addition to cutting root, you might want to cut back the top of the plants too and/or thin them out. This is best done in early spring before new growth comes. If plants are actively growing, like in later spring, Make sure they are well watered and that the air is moist- like after a rain storm when another rain is imminent. If your planters haven't quite burst at the seams, go from above with a sharp strait spade and cut down- remove the 3 inches from above and fill with fresh soil. Smaller pots like biggish house plants -remove 1-2 inches. Larger trees-remove up to 6 inches of root. Repeat every 1-3 years depending on how plants are faring. If they are drying too quick or getting leaf burn, do more often or cut more root and some top. I would do some pots every year and rotate who gets done-so you are not overwhelmed. This technique is similar to keeping bonsai. Your trees are just bigger! Some dusting of the cut roots with rock phosphate will have your plants purring.
PS. Im in Ct. on the NY border but could come out and show what to do or get work done with my partners help.