soil Changing soil in container grown plants

I've been growing habaneros for about a month for the first time and learning on the go and I think the soil they're currently in is too heavy/tightly packed (there's a empty space all around the edge of the container). I've found a better soil and was thinking on repotting them with the new soil but don't know if I should remove the old soil completely or just take the plant with the soil and pot up filling the empty space with the new soil. Should I do it without removing the soil to avoid disturbing the roots?

Turn the plant upside down while holding the soil and stem, lift off your container. Turn the hose on and wash all the dirt out of the root system. Don't touch the roots too much. Then just repot. You can spread the roots around the soil and then layer on the soil. Should bounce back in a few weeks. Just try to keep it out of direct sunlight and keep the soil moist (not soaked) until the roots take. 

There's a lot of good info here.
 
http://thehotpepper.com/topic/63081-five-year-old-potting-soil-rejuvenation/?hl=rejuvenate

Exactly what I needed, thanks! Doesn't it matter that they are small plants, the larger one being about 3 inches tall with 4 sets of true leaves?

Depends on the size of the pot, age of the plants, age of the soil (as it changes across the year), composition of the soil. In my early years I was running 5 gal pots, here in FL, on no budget so had FL 'dirt' (sand) mixed in with lots of manure and everything else I could manage to conjure up. Well the soil changes quite a bit every few months. So then if you want to keep them growing like perennials well you're kind of stuck with them so what I had some luck with was drilling tons of holes int he sides of the pots with large drill bits. The pots being black is a big part of the 'soil composition evolution' process being sped up across the year down here, the soil cooking in addition to what the plant roots etc do to alter the soil into something different from what you start with, so allowing them to breath alone was a major shft in my soil affairs so much even after dumping and shifting the sand mix crap out of my life I still went and drilled / cut slots (angle grinder) into the sides of most of my pepper pot array.

If you are changing to a potting mix that is much different than the one you have, you will want to get rid of as much of the old stuff as possible and repot a (mostly) bare root plant into the new stuff. Different soils with different structures in the same pot can create problems with watering.

This will be stressful to the plant, but if you are careful it should bounce back pretty quickly.

If you use a hose to wash off the old soil, keep it as "low power" as you possibly can. Gently running water will have less chance of damaging the fine root hairs than a strong spray will.

And make sure to keep the roots damp the entire time they are exposed. Letting them dry out even briefly during this repotting process can kill the fine root hairs. If those die, it will be much harder for your plant to continue to take up water, which will mean transplant shock or even death.