If they've been growing freely without the restriction of a pot then it wouldn't be a good idea to dig it up and cram it into a small pot. But if it's gotta be moved then make sure you put it in a big pot, use the biggest one you can find like a plastic trash can or large bucket. When you dig it up, dig a lot further than where the roots will be then take the ball of soil (plant and all) out of the ground and gently knock away the soil around the plant until you see roots. Then be careful to keep the root ball intact when you transplant it into the pot, try not to knock the soil off the roots. Put some soil into your pot, enough to raise the top of the root ball to near the top of the pot then place the plant in it. Fill in the gap around the plant with soil, firm it down with your hands but not to much and then water heavily to settle all the soil. Make sure your pot has drainage holes in the bottom. Don't do anything else to the plant after you've done this like pruning or whatever, transplanting (especially in this way) is probably the most stressful thing you can do to a plant, leave it alone until it's settled into it's new pot.