In general, you shouldn't capitalize “will”, but lately there's a fashion to do so. Whenever it appears at the beginning of a sentence (or just after a period), it should be capitalized. However, if you're just writing about the general idea, then no. If you refer to a specific document with that title, the answer is yes.
For instance, a retired lawyer 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. An executor refers to a woman who has been assigned responsibility for carrying out the provisions set out in a final will and testament. 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.