Biologists fill up libraries with their answers. If you are unfamiliar with the answers in scientific publications, no short answer will do it for you. The question, ignore science and focuses on the creation and argument of information. It is based on the assumption that DNA is information. So the question is actually this, how can accidental mistakes and random changes in a text of Shakespeare maintain, improve or expand the Shakespeare text? Well, they can't, a Shakespeare text cannot be maintained, improved or expanded by random changes. But the assumption that DNA is a book containing information is false. The ancestral molecule of RNA just behaved in a certain way for chemical reasons and life slowly assembled around it. It was not some information carried in the ancestral molecule that caused life in the first place. It was the chemical reaction of the molecule with components found on early Earth. It is the molecular structure that mattered. Specifically, what mattered the most was the ability of the ancestral molecule to make copies of itself, long before life even existed. Just like what matters with gasoline or chlorine is their molecular structure, not their brand name given by humans. Life is not an information phenomenon, but a biochemical one. DNA in living things does not store information, but biochemical potential subjected to the laws of chemistry and physics and not the laws of information. Also, it has the ability to imperfectly copy that potential. If DNA is not information, what is it? It is a very complex molecule whose structure decides its functions in living organisms. The solution is just the term we use to make sense of it as humans. When DNA is used to create a protein, it does not send info to RNA or the protein compounds. It just reacts with them chemically. There is no message, just molecules in a chemical dance. Nothing in DNA resembles Shakespeare. Every copy of a Shakespeare title contains the same information, regardless of the addition or language. However, the DNA of a species comes in countless variations. The story is unique and different for each organism. The book does not react chemically with a brain, but DNA reacts chemically with a cell. Above all, we have never observed any form of information that has the ability to make copies of itself. No book, no ink print, no kilobite has within it the ability to copy itself. DNA, however, can produce physical copies of itself because it is not information, but a weird molecule. So technically, life based on reproduction cannot be based on information. Shakespeare has a predetermined end product in mind, served by specific information. Biology does not work that way. There is no predestined scenario that DNA has to follow. DNA is matter much like any other. When it's cold enough, order freezes, but if you add salt to the water, it needs a colder environment to freeze. So its behavior towards the environment changes when its composition changes, but water contains no information. That's exactly what happens with DNA. When it changes, its behavior towards the environment of the cell changes too. The change may be beneficial for an organism, negative or neutral, or it may even be catastrophic. The change is random as it does not need to follow or receive information and natural selection guides the outcome. Those DNA sequences that natural selection permits become information only when they are printed in biology books. Prior to that, they are molecules. DNA freely copies itself in variety in perfect ways and that has varied results. Nutations can duplicate large sections of chromosomes thus introducing extra copies of a gene into a genome. Extra copies are a major source of the raw material needed for new genes to evolve. The human eye uses three genes for color vision and one for night vision. All four are descended from a single ancestral gene. New genes can be created from an ancestral gene when a duplicate copy mutates and acquires a new function. While the other copy continues to perform its original function, such processes lead to some organisms having multiple copies of their entire DNA sequence, like some plants may include even six full copies.