Changing tanks water?

I have had my 20 gal fish tank since February. I have never actually changed the water. I have about 10 different tropical fish in it including a mollie, 2 female bettas,2 gl fish,an algea eater,etc.I also have 4 dwarf frogs. HOw would I do a water chage a rock cleaning, and plant cleaning etc.? Also, where would you put all the aquatic life?