In general, you shouldn't capitalize, but lately there's a fashion to capitalize on it. The first and most obvious instance in which one should capitalize “will” is when it appears at the beginning of a sentence (or just after a period). Regardless of the context, the will is capitalized each time it is used to start a sentence. Upon closer examination, this sentence is more than likely to form a question rather than a statement describing the intention or conviction.
If you refer to a specific document with that title, the answer is yes. However, if you're just writing about the general idea, then no. A retired lawyer (and the accomplished gentleman), he had hired me to draft revisions to a rather complex Last Will and Testament. Our simple will template includes a footer that appears at the bottom of each page.
Give the title of your simple will and the page number, and include a place for you to write your initials. You must edit the footer of your copy of the simple will to add your name. Do not change the page numbers or the place of your initials. I imagine that if you were writing Last Will %26 Testament, then it would be capitalized, but if it's simply used in a sentence like the one above, it wouldn't be.
An executor refers to a woman who has been assigned responsibility for carrying out the provisions set out in a final will and will. I imagine that the only reason “last will and testament” looks good in capital letters is because it often appears as a title at the top of a will.