What will happen if you don't? What is the best way to do it?

Each House plant has its own requirements, if at all possible gently remove the plant from the pot do you see a whole lot of white or cream-colored roots going round and round or if there are roots coming out the bottom, if so it is time to repot, it is a good idea to go up 1 in. larger, teas the root's apart a little and put it in the new pot. ( one trick I learn is to take the plant out of the old pot and put a little dirt in the bottom of the new pot, than the old pot inside the new pot, pack the soil around the outer edges up to the point where the plant was, packet down well and gently twist the inner pot and lift up, just plop in your plant in the whole, this works well if you have a really full plant and you do not want a break off the leaves ) you should pick up some Root stimulator (not B1) and drenched their roots 3 times 2. weeks apart follow label instructions for mixing.