Hossfield - repotting could help a ton if your plants need it.
Growinthabudz - keep comments like that to yourself. Roots always want to expand to fuel every stage of MJ development. Unless you are going to harvest in less than a week or two, YES TRANSPLANTING COULD MAKE A BIG DIFFERENCE!
Hossfield - Your plants should have enough space to have equal mass above ground and below. If your plant sort of squished up (but not really tight) wouldn't fit in your pot you likely need a transplant.
Signs you need a transplant in soil
#1. Your soil goes dry and needs water in less than 2-3 days
#2. Roots are peeking out the drainage holes in the bottom of your pot
#3. Your plant has not grown in about 1-2 weeks.
Be careful when transplanting. Roots have tiny hairs that go off in all directions that actually feed the plant, try to disturb the dirt as little as possible. Soak the dirt your plants are in, then soak the dirt they're going to. The wetter the better, it can be almost mud. The more sticky the soil is, the better it will hold together. That will help protect your plant's root system.
Transplanting during the mid-late photoperiod can help as well. This is when the most energy is transferred above ground and in case you damage part of the root structure, a good deal of your plants mojo will be in the upper regions.
Will experienced people please flag GrowinThaBudz comment? This sort of poster can ruin people's crops.