Q: Do I need a living will if I already have a will?
A: A living will and a will are very different documents. Each provides a person with benefits but the benefits are not the same and do not overlap.
A will is a testamentary instrument that directs who receives your property after your death and designates the person who is in charge of wrapping up your affairs; your personal representative. Wills also offer other estate planning benefits such as naming a guardian for minor children and creating trusts for the benefit of a loved one.
Wills have no effect until after the maker passes away. Until that time, a will is simply a piece of paper. An important piece of paper but still just a piece of paper.
A living will is an advanced medical directive that states that in the event you are terminally ill, death will occur within a short period of time and providing medical care will only prolong the dying process, you ask that medical care be withheld. Whereas a will offers benefits following death, a living will offers benefits at the end of life.
Personally, I think that you should have both a will and an advanced medical directive. Each document addresses a specific estate planning need and neither one replaces the other.
Q: Can a person revoke a will by tearing it up?
A: When you say a "person," I'm going to assume that you mean the person who created the will. You should not destroy another person's will unless you are directed to do so by that person, and even then, don't do it.
If a maker of a will destroys it, the will is revoked. However, It's not the preferred way to revoke an existing will. The best way to revoke an existing will is to execute a new one that explicitly revokes all prior wills. The new will takes the old wills place and declares to the world that the old will is no longer valid.
If you don't want to make a new will, I suggest that you write "Revoked" across the will and tear it in half. Destroy the will in front of a couple of disinterested witnesses and keep the destroyed will. Also, notify the attorney that drafted the will so that she can note her file that the will has been revoked.
The presumption is that if the will is in the possession of the maker and it can't be located, the maker destroyed it. However, the presumption is rebuttable so if you are going to revoke your will by destroying it, make sure that there isn't any confusion about the revocation.