How to cancel a Will?

Destroying the original will certainly is possible, but as mentioned below, someone may try to probate an existing copy. So it's best to either destroy all copies (but do you really know where they all are?) or have the individual sign a codicil to that will indicating they wish their property not to pass as set forth in their will dated such and such, but instead to pass as if they had no will, per the intestacy statute of such-and-such state (presumably the state of residence). Indeed an attorney should supervise the preparation and execution of the codicil.

Prepare a new one.

All of the above are true; but I see from your profile that you refer to caring for someone with dementia. If your question relates to your friend, and that person is mentally incapacitated, I'm not sure that s/he can amend or annul an existing, valid will - I'm pretty certain that you have to be of sound mind to do this. Dementia on its own wouldn't prevent it, but it depends how advanced the dementia is. Check with whoever drafted the last one, I should.

Yes, as 1st poster said, prepare a new one. Make sure the will is dated and that it states that it nullifies all previous wills. Make sure and sign new will in front of notary. Best kept by an Attorney after that so no one can get rid of it, produce phony. You wouldn't believe what people will pull after you are gone. Saw it twice, once with my Sister, once with my Grandma. The greedy dishonest ones will try and run over the decent honest family members if you don't out smart them! :-)

DO NOT try to do anything with an existing will -- including tear it up! -- without seeking legal advice, preferably in this case from an attorney with some expertise in elder law. To make a will/revoke an old will/make a new one all requires that the maker be "of sound mind" -- that s/he have "testamentary capacity", the ability to make decisions/protect him/herself from "undue influence" and understand the consequences of the bequests being made. Depending on the stage of the disease a person with dementia may or may not have this capacity. Please seek legal advice -- there may be other things you/your friend can do, including having a phsyician attest that the person making the will DOES understand what s/he is doing.

Yes, ripping up the old one doesn't really cancel it if there are other copies. Creating a new one, or a codicil to the old one, is what makes it (or some of its provisions) null and void.

You can make a codicil to your will and make the changes or cancel the parts you want removed.

Or just rip up all copies and start over. I keep copies of my old wills as the intent through the years is quite the same and I feel it shows that more than once I have made the same choices, same for the living will. All kept in a fireproof, waterproof safe. Each child has been given instructions how to get in there.

Check your state's requirements. Some states require that the will be signed by two witnesses who are not inheriting anything, and be signed in front of a notary. In my state you are supposed to complete the whole process "without turning aside". You can look on the internet for requirements, or ask a local attorney who does wills and estates. I personally believe that writing an entire new will revoking all others is the safest way. Keep the original and several copies. You can put the original in a lock box or let an attorney keep it. Ask up front how much an attorney will charge if you want a lawyer to help you.

Attach a codicil to the present Will basically saying it is null and void. That's it. (A codicil is just a statement in writing).